ZTbe  mniversfts  of  Cbicaao 

UC-NRLF 


11    15  fl 


STUDIES  IN  MINOR  FOLDS 


A  DISSERTATION 

SUBMITTED  TO  THE   FACULTY 

OF   THE   OGDEN   GRADUATE   SCHOOL  OF   SCIENCE 

IN  CANDIDACY   FOR  THE  DEGREE   OF 

DOCTOR  OF  PHILOSOPHY 

DEPARTMENT  OF  GEOLOGY 


BY 


CHARLES  ELIJAH  DECKER 


THE  UNIVERSITY  OF  CHICAGO  PRESS 
CHICAGO,  ILLINOIS 

1920 


iERKELEY 

IBRARY 

N1VERSITY  Of 
CALIFORNIA 

EARTH 

SCIENCES 

LIBRARY 


EXCHANGE 


ZTbe  ZHmx>er8its  of  Gbicaao 


STUDIES  IN  MINOR  FOLDS 


A  DISSERTATION 

SUBMITTED   TO   THE   FACULTY 

OF   THE   OGDEN   GRADUATE   SCHOOL  OF   SCIENCE 

IN   CANDIDACY   FOR   THE   DEGREE    OF 

DOCTOR   OF   PHILOSOPHY 

DEPARTMENT  OF  GEOLOGY 


BY 

CHARLES  ELIJAH  /DECKER 


THE  UNIVERSITY  OF  CHICAGO  PRESS 
CHICAGO,  ILLINOIS 

1920 


EARTH 

SCIENCES 

IISRARY 


COPYRIGHT  1920  BY 
THE  UNIVERSITY  OF  CHICAGO 


All  Rights  Reserved 


Published  September  1920 


.      .-  ,      -•• 


Composed  and  Printed  By 

The  University  of  Chicago  Press 

Chicago.  Illinois.  U.S.A. 


CONTENTS 

PAGE 

INTRODUCTION 3 

TYPES  or  FOLDS 4 

MINOR  FOLDS  IN  ASSOCIATION  WITH  MAJOR  FOLDS 16 

FOLDS  IN  THE  MIDST  OF  HORIZONTAL  OR  GENTLY  DIPPING  STRATA     .  22 

ORIGIN  or  FOLDS 48 

NATURE  AND  ORIGIN  or  STRESSES 76 

RELATION  or  THESE  MINOR  MOVEMENTS  TO  MAJOR  MOVEMENTS  .     .  78 

SUMMARY   .  81 


433086 


LIST  OF  ILLUSTRATIONS 

PAGE 

FIG.  i.  DIAGRAM  or  A  SYMMETRICAL  ANTICLINE 5 

FIG.  2.  PHOTOGRAPH  OF  A  SYMMETRICAL  ANTICLINE 5 

FIG.  3.  DIAGRAM  or  AN  UNSYMMETRICAL  ANTICLINE 6 

FIG.  4.  PHOTOGRAPH  or  AN  UNSYMMETRICAL  ANTICLINE 6 

FIG.  5.  DIAGRAM  OF  AN  OVERTURNED  FOLD 7 

FIG.  6.  PHOTOGRAPH  OF  AN  OVERTURNED  FOLD 7 

FIG.  70.  DIAGRAM  OF  A  RECUMBENT  ANTICLINE 8 

FIG.  76.  DIAGRAM  OF  AN  OVERTURNED  FOLD  WITH  RECUMBENT  TOP  8 

FIG.  8.  PHOTOGRAPH  OF  AN  OVERTURNED  FOLD  WITH  RECUMBENT  TOP  8 

FIG.  9.  DIAGRAM  OF  A  CLOSED  ANTICLINE 10 

FIG.  10.  PHOTOGRAPH  OF  A  CLOSED  ANTICLINE 10 

FIG.  ii.  DIAGRAM  OF  AN  OPEN  FOLD n 

FIG.  12.  PHOTOGRAPH  OF  AN  OPEN  FOLD n 

FIG.  13.  AN  ERODED  DOME  IN  THE  ARBUCKLE  MOUNTAINS 12 

FIG.  14.  END  OF  AN  ERODED  DOME  IN  THE  ARBUCKLE  MOUNTAINS  12 

FIG.  15.  DIAGRAM  OF  A  SYNCLINE  BETWEEN  Two  ANTICLINES 13 

FIG.  16.  PHOTOGRAPH  OF  A  SYNCLINE  BETWEEN  Two  ANTICLINES 13 

FIG.  17.  DIAGRAM  OF  A  MONOCLINAL  FOLD 15 

FIG.  18.  PHOTOGRAPH  OF  A  MONOCLINAL  FOLD 15 

FIG.  19.  DIAGRAM  OF  PART  OF  SOUTHWEST  LIMB  OF  ARBUCKLE  ANTI- 
CLINE    20 

FIG.  20.  SYNCLINE  BETWEEN  Two  ANTICLINES  IN  ARBUCKLE  MOUN- 
TAINS   22 

FIG.  21.  PLUNGING  ANTICLINE  IN  ARBUCKLE  MOUNTAINS 22 

FIG.  22.  SMALL  INTRA-FORMATIONAL  FOLD 38 

FIG.  23.  ANTICLINE  HAVING  Axis  PARALLEL  WITH  VALLEY 39 

FIG.  24.  ANTICLINE  AT  NORTH  EDGE  OF  MEADVILLE,  PA 39 

FIG.  25.  UNSYMMETRICAL  ANTICLINE  NEAR  GIRARD,  PA 40 

FIG.  26.  ANTICLINE  NEAR  NORTH  EAST,  PA 40 

FIG.  27.  ANTICLINAL  FOLD  WITH  UNERODED  CREST. 42 

FIG.  28.  SMALL  ANTICLINE  ALONG  ELK  CREEK 42 

FIG.  29.  THRUST  FAULT  ALONG  LITTLE  ELK  CREEK 44 

FIG.  30.  THRUST  FAULT  ALONG  SIXTEEN  MILE  CREEK 44 


viii  LIST  OF  ILLUSTRATIONS 

PAGE 

FIG.   31.  THRUST  FAULT  NEAR  GIRARD,  PA 45 

FIG.   32.  THRUST  FAULT  ALONG  WALNUT  CREEK 45 

FIG.   33.  UNSYMMETRICAL  FOLD  WITH  Two  THRUST  FAULTS 46 

FIG.   34.  Two  THRUST  FAULTS  WITH  SMALL  FOLD  BETWEEN 46 

FIG.   35.  Two  SMALL  FOLDS  IN  OPEN  COAL  MINE 66 

FIG.   36.  SMALL  FOLDS  IN  SHALE  NEAR  DUNKIRK,  N.Y 66 

FIG.   37.  RIDGE  ON  TERRACE  ABOVE  FOLD ; 71 

FIG.   38.  FOLD  DEFORMING  A  FORTY-THREE-FOOT  TERRACE 71 

FIG.   39.  ANTICLINE  WITH  ERODED  CREST  NEAR  PROSPECT,  N.Y 72 

FIG.   40.  FOLD  WITH  ERODED  CREST  NEAR  KINGSVILLE,  OHIO 72 

FIG.   41.  FOLD  WITH  CREST  UNERODED  IN  TWENTY-FOOT  TERRACE...  73 

FIG.   42.  FOLD  WITH  CREST  UNERODED  IN  Low  TERRACE 73 

FIG.   43.  FAULT  WITH  TOP  ERODED 75 

FIG.   44.  FAULT  WITH  TOP  UNERODED 75 

PLATE      I.     GENERAL  MAP  OF  EASTERN  LAKE  REGION facing    3 

PLATE    II.     GENERAL  MAP  OF  OKLAHOMA facing  17 

PLATE  III.    ISOBASES  OF  DEFORMED  PENEPLAIN  AND  OF  UPLIFT 

TO  NORTHEAST facing  81 


LIST  OF  TABLES 

TABLE  PAGE 

I. — PALEOZOIC  FORMATIONS  OF  OKLAHOMA 18 

II. — PALEOZOIC  FORMATIONS  OF  PENNSYLVANIA  AND  NEW  YORK 25 

III. — LOWER  DEVONIAN  AND  UPPER  MISSISSIPPIAN  FORMATIONS 27 

IV. — PORTAGE  GROUP 28 

V. — TREND  OF  AXES  IN  LAKE  REGION 80 

VI. — TREND  OF  AXES  AT  NORTHWEST  EDGE  OF  APPALACHIANS  . .  80 


OUTLINE 

INTRODUCTION 

TYPES  or  FOLDS 

Symmetrical  Anticline 

Unsymmetrical  Anticline 

Overturned  Anticline 

Recumbent  Fold 

Closed  Anticline 

Open  Anticline 

Dome 

Syncline 

Isoclinal  Folds 

Anticlinoria  and  Synclinoria 

Monoclinal  Fold 

MINOR  FOLDS  IN  ASSOCIATION  WITH  MAJOR  FOLDS 
General  Relations  and  Direction  of  Axes 
Minor  Folds  in  the  Arbuckle  and  Wichita  Mountains  of  Oklahoma 

Igneous  Rocks 

Sedimentary  Rocks 

Structure  of  Rocks 

Types  of  Folds 

Summary 

FOLDS  IN  THE  MIDST  OF  HORIZONTAL  OR  GENTLY  DIPPING  STRATA 
Location  and  Area 
Topography  of  the  Area 
Lake  Plain 
Upland  Plain 
Stratigraphy 

Ordovician  Formations 

Beekmantown  Limestone 
Lowville  Limestone 
Trenton  Limestone 
Queenston  Shale 
Upper  Devonian 
Portage  Group 
Huron  Shale 
Girard  Shales 
Chagrin  Formation 
Chemung  Formation 
Cleveland  Shale 
Cattaraugus  Formation 


STUDIES  IN  MINOR  FOLDS 

Devono-Carboniferous  Formations 
Riceville  Shale 
Oswayo  Formation 

Mississippian  Formation 
Bedford  Shales 

Pennsylvanian  Formation 

Sharon  or  Olean  Conglomerate 

Quaternary  Deposits 
Pleistocene 
Post-glacial 
Geologic  History 
Physiographic  History 

Glacial  Erosion 

Glacial  Deposition 

Drainage  Changes 

Glacio-Lacustrine  Substage 

Post-glacial  Changes 
Structure  of  the  Rocks 

General  Structure 

Local  Structure 
General  Types  of  Folds 

Intra-formational  Folds 

Parallel  Folds 

Transverse  Folds 
Faults 

Unrelated  to  Folds 

Related  to  Folds 
Origin  of  Folds  and  Faults 

Igneous  Activity  and  Heat  from  Molten  Rock 

Rise  in  Temperature  at  Close  of  Glacial  Period 

Pressure  Due  to  Expansion  of  Ice 

Alteration  of  Iron  Sulphides 

Weathering  of  Rocks 

Crystallization  of  Limestone 

Solution  of  Rocks  beneath  the  Surface* 

Shrinkage  by  Compacting  Soft  Rocks 

Pressure  of  Valley  Walls 

Relief  from  Compression 

Weight  of  Delta 

Landslides 

Pressure  of  Natural  Gas 

Differential  Movement 

Glaciation 

Drag  of  Icebergs 


STUDIES  IN  MINOR  FOLDS  3 

Tangential  Compression 
Summary  of  Origin  of  Folds 
Age  of  Folds  and  Faults 
Pre-glacial 
Glacial 
Post-glacial 

NATURE  AND  ORIGIN  OF  STRESSES 
General  Cumulative  Stresses 
General  Residual  Stresses 

RELATION  or  THESE  MINOR  MOVEMENTS  TO  MAJOR  MOVEMENTS 
Tilting  to  the  Northeast 
Doming  of  Harrisburg  Peneplain 

SUMMARY 

INTRODUCTION 

The  data  on  which  these  studies  are  based  have  been  secured  from 
a  narrow  area  south  of  Lake  Erie,  extending  from  Cleveland  across 
northeastern  Ohio,  northwestern  Pennsylvania,  and  into  New  York  as 
far  as  Dunkirk  (see  Plate  I) .  A  few  folds  on  Lake  Ontario  were  studied, 
both  in  northern  New  York  and  southern  Canada.  A  number  of  inter- 
mediate points  between  Niagara  and  Dunkirk  were  visited,  as  were  several 
others  farther  southeast  in  New  York  and  westward  from  Cleveland  to 
Sandusky,  Ohio.  A  few  folds  were  studied  in  the  folded  areas  of  the 
Arbuckle  and  the  Wichita  mountains  of  Oklahoma. 

In  geological  literature  much  attention  has  been  given  to  structural 
studies,  especially  to  folds  and  folded  regions.  However,  the  major 
folds  have  seemed  so  to  overshadow  the  minor  ones  that  the  latter  have 
been  passed  over,  being  considered  relatively  unimportant.  Economic 
considerations  have  directed  attention  to  some  minor  folds  which 
received  no  consideration  as  having  any  importance  from  a  structural 
standpoint.  Of  the  folds  of  this  type,  some  of  the  most  noteworthy  are 
those  in  Pennsylvania,  West  Virginia,  and  Oklahoma  for  oil  and  gas, 
Wisconsin  for  lead  and  zinc,  Michigan  and  Wisconsin  for  iron,  and 
Australia  for  gold. 

It  is  the  purpose  in  this  paper  to  illustrate  by  diagrams  and  photo- 
graphs a  series  of  types  of  minor  folds;  to  illustrate  and  study  briefly  a 
few  minor  folds  in  their  relation  to  major  ones;  to  illustrate  a  larger 
number  of  small  folds  in  the  midst  of  horizontal  or  gently  dipping 
strata,  showing  their  characteristics,  methods  of  origin,  age,  and  relation 
to  faults;  and  finally,  to  connect  these  minor  deformations,  in  so  far  as 


4  STUDIES  IN  MINOR  FOLDS 

possible,  with  larger  movements,  and  show  their  significance,  as  indi- 
cating the  presence  of  compressional  stresses  in  the  rocks  in  the  interim 
between  the  great  periods  of  deformation  and  mountain-building. 

The  writer  makes  grateful  acknowledgment  for  direction  and  help  to 
Professor  R.  D.  Salisbury,  under  whose  supervision  this  study  has  been 
pursued,  to  Professor  T.  C.  Chamberlin  for  helpful  suggestions,  to 
Professor  R.  T.  Chamberlin  for  valuable  criticisms  and  suggestions, 
to  Frank  Gahrtz  for  work  on  figures  and  maps,  and  to  W.  E.  Coon  for 
field  assistance. 

TYPES    OF   FOLDS 

The  most  common  type  of  fold  is  the  anticline.  Gilbert  has  defined 
it  as  one  in  which  the  strata  dip  in  two  directions  away  from  the  axis.1 
Anticlines  are  extremely  variable  in  form,  so  that  a  number  of  distinct 
types  have  been  recognized.  These  types  are  symmetrical,  unsymmet- 
rical,  overturned,  recumbent,  open,  and  closed  folds,  besides  the  com- 
pound form — the  anticlinorium. 

Symmetrical  anticline. — A  symmetrical  anticline  is  a  fold  whose  axial 
plane  is  vertical  and  on  which  the  dip  at  corresponding  points  on  the 
two  limbs  is  equal.  A  diagram  of  a  symmetrical  fold  is  shown  in 
Figure  i.  In  this  figure  cd  is  a  line  in  the  axial  plane  which  divides 
the  anticline  into  two  equal  and  symmetrical  limbs.  The  fold  is  rep- 
resented as  having  the  crest  eroded  and  restored  by  the  dashed  lines. 
Examples  of  folds  of  this  general  type  were  found  near  Westfield,  New 
York;  North  East,  Erie,  Girard,  and  Meadville,  Pennsylvania;  and 
Andover,  Conneaut,  Kingsville,  and  Painesville,  Ohio.  A  fold  of  this 
type  which,  however,  is  not  perfectly  symmetrical,  is  shown  in  Figure  2. 
It  crosses  the  bed  of  Walnut  Creek  5  miles  south  of  Erie,  Pennsylvania. 
The  dip  to  the  west  is  14°  and  to  the  east  is  1 7°.  The  axis  trends  N.  io°W. 
The  beds  vary  in  thickness  from  2  to  7  inches,  and  consist  chiefly  of 
blue  shale  with  some  sandy  beds  interspersed.  The  stream  has  eroded 
the  crest  of  the  fold,  cutting  deeply  into  the  axis  forming  the  basin  for 
the  pool  in  the  foreground.  The  loose  material  on  top  of  the  fold  is 
shingle,  contributed  largely  by  the  tributary  which  enters  at  the  left 
of  the  crest.  A  more  perfectly  symmetrical  fold  is  shown  in  Figure  31, 
in  which  the  dip  is  8°  in  each  limb.  Among  the  other  folds  of  this  type 
mentioned  above,  some  of  those  near  Conneaut  and  Painesville  are  more 
gentle  and  open,  while  some  near  Westfield,  Andover,  and  Meadville  are 
smaller  and  more  closed. 

1  G.  K.  Gilbert,  Amer.  Jour.  Sci.,  3d  Ser.,  XII  (1876),  21. 


STUDIES  IN  MINOR  FOLDS  5 

Unsymmetrical  anticline. — An  unsymmetrical  anticline  is  a  fold  in 
which  the  axial  plane  is  inclined  and  in  which  the  strata  dip  more  steeply 
in  one  limb  than  in  the  other.  A  diagram  of  a  fold  of  this  type  is  shown 
in  Figure  3.  In  this  figure  the  line  cd  marks  the  inclined  axial  plane 
which  divides  the  fold  into  two  very  unsymmetrical  parts.  The  dip  in 


FIG.  i. — Diagram  of  a  symmetrical  anticline  from  which  the  crest  has  been 
eroded.     Restoration  of  the  eroded  part  is  shown  by  dotted  lines. 


FIG.  2. — Photograph  of   a   symmetrical  anticline  in  the  bed  of  Walnut  Creek, 
5  miles  south  of  Erie,  Pa. 

the  limb  at  the  right  is  much  greater  than  in  the  one  at  the  left.  A 
fold  of  this  type  deforms  the  west  bank  of  the  Chagrin  River,  a  mile 
west  of  Chagrin  Falls,  Ohio.  Figure  4  is  a  photograph  of  this  fold. 
The  steep  dip  downstream  to  the  northeast  is  29°,  and  the  gentler  dip 
upstream  is  11°.  The  fold  is  about  160  feet  wide,  and  deforms  the  rocks 
of  a  terrace  56  feet  high.  The  rocks  consist  of  alternating  sandstones 


6 


STUDIES  IN  MINOR  FOLDS 


and  shales  in  the  Bedford  formation.1  (See  Table  III.)  The  heavy 
sandstone  bed,  which  stands  out  clearly  in  the  picture,  is  17  inches 
in  thickness.  This  bed  has  been  slightly  faulted  at  the  crest  of  the 
fold,  the  horizontal  displacement  being  2  feet  and  10  inches.  The  dis- 
tinctness of  the  brecciated  zone  above  this  stratum  suggests  that  the 


FIG.  3. — Diagram  of  an  unsymmetrical  anticline 


FIG.  4. — Photograph  of  an  unsymmetrical  anticline  near  Chagrin  Falls,  Ohio 

remaining  strata  above  were  affected  by  this  fracture.  While  the  steep 
side  of  the  bank  is  weathered  and  partially  covered  with  vegetation,  the 
fact  that  a  path  was  started  from  the  top  of  the  terrace  along  a  natural 
depression  in  the  line  of  the  axis  seems  to  be  another  indication  that 
the  fault  affects  all  of  the  uppermost  strata.  Here,  then,  a  fold  below 
1  C.  H.  Prosser,  Geol.  Surv.  Ohio  Bull.  15,  4th  Ser.  (1912),  pp.  197,  198. 


STUDIES  IN  MINOR  FOLDS  7 

passes  into  a  fault  above.1  This  same  relation  of  fold  and  fault  was 
found  25  miles  to  the  northeast  along  Paine  Creek.  This  anticline  is 
only  one  of  a  large  number  with  marked  asymmetry  that  exist  in  the 
area.  Two  distinct  examples  of  this  type  occur  within  half  a  mile  of 


FIG.  5. — Diagram  of  an  overturned  fold 


Fig.  6. — An  overturned  fold  on  the  northwest  shore  of  Lake  Ontario  near  Bur- 
lington, Ontario. 

each  other  near  Girard,  Pennsylvania,  and  in  them  the  highly  inclined 
limbs  are  toward  one  another. 

Overturned  anticline. — When  the  stress  or  resistance  differs  greatly 
on  the  opposite  sides  of  a  fold,  the  strata  on  one  side  are  raised  and  the 

1  Chamberlin  and  Salisbury,  Geology,  I  (1905),  516,  Fig.  121;   and  Bailey  Willis, 
Thirteenth  Ann.  Kept.  U.S.G.S.,  Part  II  (1893),  Plates  79,  93,  94. 


8 


STUDIES  IN  MINOR  FOLDS 


top  of  the  fold  is  thrust  forward  and  bent  over  until  the  strata  on  both 
sides  of  the  axis  dip  in  the  same  general  direction.  By  this  process  the 
overturned  anticline  is  formed.  Figure  5  is  a  diagram  of  an  overturned 
fold.  The  axis  is  bent  to  the  right  to  such  an  extent  that  the  younger 
beds  beneath  the  axis  have  their  dips  reversed  toward  the  left,  or  in  the 


FIG.  7a. — Diagram  of  a  recumbent  anticline  (after  Van  Hise) 
FIG.  76. — Diagram  of  an  overturned  fold  with  recumbent  top 


FIG.  8. — An  overturned  fold  with  recumbent  top,  near  North  East,  Pa. 

same  general  direction  as  those  above  the  axis.  Figure  6  shows  an 
overturned  anticline  in  the  sandy  shales  on  the  northwest  shore  of 
Lake  Ontario,  8  miles  northeast  of  Burlington,  Ontario.  The  fold  is 
in  the  uppermost  shales  in  a  1 4-foot  terrace,  and  the  strata  in  the  over- 
turn are  thrust  up  into  the  terrace  material  in  a  way  to  indicate  the 
recency  of  the  fold.  This  is  one  of  several  small  folds  above  the  end  of 
a  thrust  fault  whose  plane  has  the  low  angle  of  5°  to  14°.  Two  other 


STUDIES  IN  MINOR  FOLDS  9 

overturned  folds  were  found  in  northern  Ohio,  one  3  miles  south  of 
Willoughby,  along  the  Chagrin  River,  and  one  6  miles  southwest  of 
Conneaut,  along  Conneaut  Creek.  On  the  south  side  of  Lake  Ontario, 
at  Thirty  Mile  Point,  there  is  an  anticline  with  overturned  axis.  The 
overturned  top  of  the  fold  incloses  glacial  drift  beneath  it.  This  fold  is 
shown  in  Plate  19  in  the  back  of  the  Niagara  Folio. 

Recumbent  fold. — When  an  anticline  is  so  far  overturned  tjiat  the 
inverted  strata  approach  a  horizontal  position,1  it  is  called  a  recumbent 
fold.  A  diagram  of  such  a  fold  is  shown  in  Figure  ja.  This  is  taken 
from  Van  Hise,  who  in  his  article  on  "North  American  Pre-Cambrian 
Geology"  gives  an  excellent  discussion  of  the  various  types  of  folds.2 
No  fold  closely  approaching  the  form  of  the  one  in  Figure  7  a  was 
found  in  the  area  studied,  but  Figure  7 b  is  a  diagram  of  one  one-fourth 
mile  south  of  North  East,  Pennsylvania,  on  the  east  side  of  Sixteen  Mile 
Gulf.  The  notebooks  in  the  photograph  of  the  same  fold  (Fig.  8),  one 
on  the  axis  and  one  down  in  the  right  foreground,  are  on  the  same 
stratum.  By  referring  to  Figure  jb,  it  will  be  seen  that  the  strata 
have  been  broken  at  the  base  of  the  right  limb  and  overthrust  to  the 
right.  In  this  figure  the  bed  beneath  e  has  its  continuation  at/g.  This 
is  the  only  example  of  a  fold  found  in  this  area  approaching  the  recum- 
bent type  at  all  closely. 

Closed  anticlinal  fold. — A  closed  anticline  is  one  in  which  the  limbs 
are  pressed  closely  together.  With  reference  to  position  of  axial  plane 
a  closed  fold  may  be  upright,  overturned,  or  recumbent.  A  diagram  of 
an  upright  closed  anticline  is  shown  in  Figure  9,  and  a  photograph  of 
one  in  Figure  10.  This  is  the  central  part  of  a  much  larger  fold,  several 
of  which  are  associated  here  on  the  flank  of  a  very  much  larger  anti- 
cline. For  several  feet  from  the  crest  the  strata  are  parallel,  as  they 
are  continuously  in  the  carinate  fold.  A  short  distance  from  the  top, 
however,  the  strata  begin  to  diverge.  This  fold  is  in  the  midst  of  a 
folded  area,  in  the  thin  beds  of  the  Simpson  formation  in  the  Arbuckle 
Mountains,  one-fourth  mile  below  Crusher,  Oklahoma.  No  folds  as 
close  as  this  were  found  in  the  Great  Lakes  region,  though  several 
approach  the  closed  condition. 

Open  anticline. — An  open  anticline  is  one  in  which  the  strata  spread 
widely  from  the  axial  plane.  Open  folds  may  have  the  axial  plane 
vertical  or  inclined.  In  Figure  n  a  diagram  is  given  of  a  gentle,  open 
fold.  The  strata  swing  up  in  broad,  open  curves,  and  the  dip  is  slight 

1  Bailey  Willis,  op.  cit.,  p.  221. 

2  C.  R.  Van  Hise,  Sixteenth  Ann.  Kept.  U.S.G.S.,  Part  I  (1895),  pp.  581-843. 


10 


STUDIES  IN  MINOR  FOLDS 


from  the  axis  on  either  side.     The    photograph  of    such  an  anticline  is 
shown  in  Figure  12.     It  is  in  the  east  bank  of  Big  Creek,  3  miles  south- 


FIG.  9. — Diagram  of  a  closed  anticline 


FIG.  10. — Closed  anticline  in  Simpson  formation  near  Crusher  in  the  Arbuckle 
Mountains,  Okla. 

east  of  Painesville,  Ohio.      The  fold  is  60  feet  wide,  has  a  rise  of  4^  feet 
at  the  crest,  and  the  dip  is  12°  on  either  side.     The  strike  of  the  beds, 


STUDIES  IN  MINOR  FOLDS 


II 


of  N:35°W.,  and  the  direction  of  the  axis,  are  well  shown  by  the  fall  of 
the  creek  over  the  southwest  limb.  A  sandy  bed  15  inches  thick  in  the 
midst  of  the  shales  is  the  cause  of  the  fall,  and  this  resistant  bed  stands 
out  near  the  base  of  the  bank,  showing  clearly  the  form  of  the  fold.  A 
large  number  of  folds  of  this  type  were  found,  some  larger,  some  smaller. 


FIG.  ii. — Diagram  of  a  gentle  open  fold 


FIG.  12. — Photograph  of  a  gentle  open  fold  along  Big  Creek,  near  Painesville, 
Ohio. 

Most  of  the  large,  open  ones  seem  to  belong  to  the  earlier  periods  of 
folding,  for  in  connection  with  the  large  open  folds  no  evidence  was 
found  to  indicate  that  any  of  them  were  as  recent  as  the  glacial  period. 
Dome. — A  dome  is  an  anticline  in  which  the  strata  dip  in  all  direc- 
tions from  the  center,  or  one  with  quaquaversal  dip.  A  dome  may  be 
either  circular  or  elongate.  No  domes  were  studied  in  the  eastern  area, 
but  one  was  found  in  the  Arbuckle  Mountains  of  Oklahoma,  occurring 


12 


STUDIES  IN  MINOR  FOLDS 


in  the  Arbuckle  limestone  at  the  head  of  Falls  Creek  (Figs.  13  and  14). 
Numerous  larger  domes  occur  in  the  Henry  Mountains  of  Utah,1  in  the 
Piedmont  region  of  Maryland,2  and  in  eastern  Wyoming3 — the  Black 


FIG.  13. — An  eroded  dome  in  the  Arbuckte  limestone  near  the  head  of  Falls 
Creek,  Arbuckle  Mountains,  Okla. 


FIG.  14. — A  view  of  the  dome  in  Figure  13  taken  across  the  front  foreground  in 
the  bed  of  the  creek.     The  deep  hole  at  the  left  is  in  the  crest. 

1  G.  K.  Gilbert,  "Henry  Mountains,"  U.S.G.S.  (1877),  Plates  II  and  IV. 

2  E.  B.  Mathews,  Johns  Hopkins  University  Circular,  New  Series,  No.  7  (1907), 
pp.  27-34. 

*  Sundance  Folio,  No.  127  (1905),  "Structure  Section  Sheet." 


STUDIES  IN  MINOR  FOLDS  13 

Hills  themselves  being  a  large  dome.1  A  dome  of  the  elongate  type, 
truncated  by  erosion,  occurs  in  the  Niagara  limestone  at  Stony  Island. 
This  dome,  in  the  southern  part  of  Chicago,  was  an  island  at  the  late 
stage  of  Lake  Chicago  (the  predecessor  of  Lake  Michigan),  when  the 
outlet  was  to  the  southwest  through  the  Des  Plaines  and  Illinois  rivers. 


cL 

FIG.  15. — Diagram  of  a  syncline  between  two  anticlines 


FIG.  1 6. — Syncline  between  two  anticlines  near  Andover,  Ohio 

Syncline. — The  syncline  is  the  reverse  of  an  anticline.  According 
to  Gilbert  the  strata  in  it  dip  in  two  directions  toward  the  axis.2  A 
single  stratum  dipping  from  both  sides  toward  the  axial  plane  forms  a 
basin.  And  as  the  top  of  the  anticline  is  called  the  crest,  so  the  bottom 
of  the  syncline  is  called  the  trough.  As  in  anticlines,  so  in  synclines 
the  axial  planes  may  be  vertical  or  inclined,  and  the  fold  may  be  open 

1  N.  H.  Darton,  Prof.  Paper  No.  65  (1909),  p.  62. 

2  G.  K.  Gilbert,  Amer.  Jour.  Sci.,  3d  Ser.,  XII  (1876),  21. 


14  STUDIES  IN  MINOR  FOLDS 

or  closed.  Figure  15  shows  a  diagram  of  a  syncline  between  two  anti- 
clines. The  axes  of  the  anticlines  are  marked  by  the  lines  ab  and  cd. 
The  axial  plane  of  the  syncline  lies  about  halfway  between.  There  are 
three  small  anticlines  with  two  intervening  synclines  on  the  north  side 
of  a  small  stream  at  the  southern  edge  of  the  Andover  quadrangle, 
Ohio.  They  are  upstream  a  few  rods  east  of  the  Lake  Shore  and  Michi- 
gan Southern  Railway.  A  photograph  of  one  of  these  synclines  and  two 
of  the  anticlines  is  shown  in  Figure  16.  While  several  synclines  were 
found,  there  were  very  few  as  compared  with  the  number  of  anticlines. 

Isoclinal  or  carinate  folds. — When  a  series  of  folds  is  so  closely 
compressed  that  the  strata  in  the  limbs  are  all  parallel,  they  are  called 
isoclinal,  and  carinate  is  the  name  given  to  a  single  fold  of  this  type, 
No  isoclinal  folds  were  found. 

Anticlinoria  and  synclinoria. — When  the  large  anticlines  and  syn- 
clines have  within  them  a  series  of  smaller  folds,  they  are  called  anti- 
clinoria  and  synclinoria.  Compound  folds  of  this  type  are  found  in  the 
Arbuckle  Mountains,1  but  the  larger  ones  are  far  too  great  in  extent  to 
get  within  the  compass  of  a  photograph.  However,  both  in  these 
mountains  and  in  the  Wichitas,  smaller  anticlinoria  and  synclinoria 
commonly  have  plunging  axes,  so  the  structure  is  shown  by  the  edges 
of  the  strata  that  protrude  in  the  plateaus.  (See  Fig.  21.)  In  the 
eastern  area  near  the  Great  Lakes,  anticlines  and  synclines  are  associ- 
ated in  a  number  of  places,  but  not  in  the  form  typical  of  the  anti- 
clinoria and  synclinoria.  A  part  of  a  series  of  anticlines  and  synclines 
is  seen  in  Figure  16.  The  fold  shown  in  Figure  8  is  adjacent  to  a  larger 
anticline  which  has  another  sharp  fold  at  the  opposite  end  of  it.  Other 
examples  of  the  association  of  anticlines  and  synclines  are  found  along 
Elk  Creek  near  Girard,  Pennsylvania.  In  these  instances,  however,  no 
larger  fold  seems  to  dominate  them  to  give  them  the  form  of  anti- 
clinoria or  synclinoria. 

Monoclinal  fold. — "A  monoclinal  fold  is  a  double  flexure,  connect- 
ing strata  at  one  level  with  the  same  strata  at  another  level."2  It  has 
one  less  flexure  than  the  anticline.  Figure  17  shows  a  diagram  of  a 
monoclinal  fold  in  which  the  double  flexure,  marked  by  the  lines  cd  and 
ef,  joins  the  strata  above  with  the  same  strata  at  the  right  below.  A 
fold  of  this  type  is  shown  in  Figure  18.  This  fold  is  in  the  flaggy  Che- 
mung  sandstones  and  shales  along  Sixteen  Mile  Creek,  three-fourths  of 
a  mile  northwest  of  North  East,  Pennsylvania.  It  deforms  the  fourteen- 

1  C.  A.  Reeds,  Okla.  Geol.  Surv.  Bull.  3  (1910),  pp.  51-53. 

2  G.  K.  Gilbert,  Amer.  Jour.  Sci.,  3d  Ser.,  XII  (1876),  21. 


STUDIES  IN  MINOR  FOLDS  15 

foot  terrace,  and  the  loose  shales  at  the  top  are  uneroded.  The  mono- 
clinal fold  so  common  in  the  Colorado  plateaus1  is  uncommon  in  this 
area,  only  a  few  others  having  been  found. 

The  term  monoclinal  has  been  used  with  two  other  distinct  mean- 
ings.    The  most  common  use  is  to  express  the  structure  of  the  rocks 


e 

FIG.  17. — Diagram  of  a  monoclinal  fold 


FIG.  1 8. — A  monoclinal  fold  near  North  East,  Pa. 

in  an  area  in  which  the  formations  of  a  series  are  inclined  in  a  single 
direction,  irrespective  of  the  manner  in  which  the  dip  was  acquired. 
Thus  the  structure  on  one  side  of  an  eroded  dome  is  called  a  monocline.2 
The  structure  of  the  eastward  dipping  rocks  of  the  Connecticut  Valley 

1  G.  K.  Gilbert,  ibid.,  p.  21. 

2  Belle  F our che  Folio,  South  Dakota  (1909),  p.  5. 


16  STUDIES  IN  MINOR  FOLDS 

is  called  monoclinal.1  The  ridges  formed  by  the  resistant  formations 
on  one  side  of  an  eroded  anticline  are  called  monoclinal  ridges.2  The 
third  sense  in  which  the  term  monoclinal  has  been  used  is  to  describe  a 
series  of  folds  in  wh.ich  the  axes  all  are  parallel.  Van  Hise  has  called 
a  series  of  folds  with  parallel  axial  planes  monoclinal  folds.3  "Homo- 
cline"  has  been  suggested  by  R.  A.  Daly  as  a  substitute  for  monocline. 
He  says: 

For  convenience  the  word  homocline  will  be  used  as  a  general  name  for 
any  block  of  bedded  rocks  all  dipping  in  the  same  direction.  The  writer  is 
inclined  to  follow  the  general,  though  not  universal  usage  which  defines  mono- 
cline as  a  one-limbed  flexure  in  strata,  which  are  usually  flat-lying  except  in 
the  flexure  itself.  A  homocline  may  be  a  monocline,  an  isocline,  a  tilted  fault 
block,  or  one  limb  of  an  anticline  or  syncline.4 

This  seems  simply  a  multiplication  of  terms  in  suggesting  another  one 
for  the  most  common  usage  for  monocline.  Monoclines  readily  could 
be  distinguished  as  to  origin  by  one  of  the  prefixes  tilt-,  syn-,  anti-, 
block-,  or  fault-. 

MINOR   FOLDS   IN   ASSOCIATION   WITH   MAJOR   FOLDS 

General  relations  and  direction  of  axes. — In  areas  of  folded  rocks, 
smaller  folds  are  commonly  associated  with  the  larger  folds,  and  not 
infrequently  folds  of  several  orders  are  found  together.  Bascom  has 
recognized  folds  of  four  orders  associated  in  the  Piedmont  district  of 
Pennsylvania.5  The  minor  folds  may  occur  on  or  among  the  major 
ones,  or  they  may  occur  adjacent  to  the  major  ones,  on  either  or  both 
sides.  With  reference  to  the  trend  of  axes,  in  some  instances  the  axes 
of  the  minor  folds  are  approximately  parallel  with  those  of  the  major 
ones.  Mathews  and  Miller  describe  an  area  in  north  central  Maryland 
in  which  the  minor  sharp  folds  are  parallel  with  the  major  open  ones.6 
This  parallelism  seems  to  indicate  that  the  minor  folds  are  related 
definitely  to  the  major  folds.  Second,  the  axes  of  the  minor  folds  may 
be  transverse  to  those  of  the  major  folds.  Those  mentioned  above, 
described  by  Bascom,  are  of  this  type:  Here  the  major  and  minor 
folds  seem  unrelated.  And  third,  the  direction  of  axes  of  minor  folds 

1  Chamberlin  and  Salisbury,  Earth  History,  III  (1906),  n. 

2  J.  W.  Powell,  Amer.  Jour.  Sci.,  ad  Ser.,  XII  (1876),  416. 

3C.  R.  Van  Hise,  Ann.  Kept.  U.S.G.S.,  XVI,  Part  I  (1895),  621;  Fig.  134, 
658;  and  Fig.  148,  801. 

4  R.  A.  Daly,  Canada  Dept.  Mines  Geol.  Surv.,  Mem.  68  (1915),  p.  53,  note. 

s  F.  Bascom,  Bull.  Geol.  Soc.  Amer.,  XVI  (1905),  306-8. 

6  E.  B.  Mathews  and  W.  J.  Miller,  Bull.  Geol.  Soc.  Amer.,  XVI  (1905),  362. 


STUDIES  IN  MINOR  FOLDS  17 

may  be  extremely  variable,  making  their  relation  to  the  major  folds 
uncertain.  In  describing  the  structure  of  southeastern  Alaska,  Brooks 
says  the  main  trend  of  the  major  structures  is  northwest  and  southeast, 
but  the  axes  of  the  minor  folds  are  extremely  variable  in  direction.1 

Minor  folds  in  the  Wichita  and  Arbuckle  mountains  of  Oklahoma. — 
To  show  some  of  the  relations  of  minor  to  major  folds,  a  few  illustra- 
tions will  be  given  from  the  Arbuckle  and  Wichita  mountains  of  Okla- 
homa. These  mountains  are  in  two  separate  groups  in  the  southern 
part  of  the  state,  the  Wichitas  being  about  60  miles  northwest  of  the 
Arbuckles.  (See  Plate  II.)  Each  group  is  about  60  miles  long  and 
about  twice  as  long  as  wide,  the  longer  axes  extending  in  a  general  east- 
west  direction.  The  Arbuckles  are  the  lower,  the  highest  part,  at  the 
northwest,  rising  about  400  feet  above  the  surrounding  plains  to  a  total 
of  about  1,300  feet.  The  highest  peaks  in  the  Wichitas  rise  about  1,500 
feet  above  the  plain,  to  a  total  height  of  a  little  less  than  2,500  feet.2 

Igneous  rocks. — Both  .the  Arbuckle  and  Wichita  mountains  consist 
of  central  masses  of  igneous  rocks  surrounded  by  great  thickness  of 
sedimentary  formations. 

In  the  Arbuckle  Mountains  there  are  three  areas  of  igneous  rocks. 
A  large  area  in  the  southeastern  part,  of  about  148  square  miles,  con- 
sists chiefly  of  granite  with  minor  amounts  of  quartz-monzonite  and 
dikes  of  diabase,  aplite,  and  pegmatite.  The  other  two  areas  are  com- 
paratively small  ones,  together  being  about  7  square  miles  in  extent,  in 
the  northwestern  part  of  the  mountains.3  These  areas  consist  of  por- 
phyry with  some  basalt  and  diabase  dikes.  The  predominance  of  acidic 
rocks  in  the  Arbuckle  Mountains  is  marked,  as  the  basic  type  is  limited 
largely  to  dikes. 

In  the  Wichita  Mountains  the  igneous  rocks  form  a  large  elongate 
central  mass  around  which  are  numerous  scattered  areas,  particularly 
to  the  southwest  and  northwest.  While  granites  and  porphyries  pre- 
dominate, there  are,  besides  the  dikes  of  basalt  and  diabase,  very  large 
areas  of  gabbro,  so  there  is  a  very  much  larger  amount  of  basic  rock  in 
the  Wichitas  than  in  the  Arbuckles.  In  both  groups  of  mountains  the 
igneous  rocks  are  pre-Cambrian  in  age.  Against  these  massive  igneous 
rocks  the  sedimentary  formations  have  been  folded. 

1  F.  H.  Brooks,  U.S.G.S.  Prof.  Paper  31  (1904),  p.  29. 

2  J.  A.  Taff,  U.S.G.S.  Prof.  Paper  31  (1904),  p.  54. 

3  C.  A.  Reeds,  Okla.  Geol.  Surv.  Bull.  3  (1910),  pp.  31-32. 


i8 


STUDIES  IN  MINOR  FOLDS 


TABLE  I 

PALEOZOIC   FORMATIONS   OF   THE   ARBUCKLE   MOUNTAINS,   OKLAHOMA 


System 

Permian 
Pennsylvanian 

Mississippian 


Devonian 


Silurian 


Ordovician 

Upper  Cambrian 
Middle  Cambrian 


(Modified  from  Wallis)1 

Formations 

Red  beds 

Franks  conglomerate 
f  Caney  shale 
\  Sycamore  limestone 

Woodford  chert 
(Hiatus) 

Bois  d'Arc  limestone 

Haragan  marl 
(Hiatus) 

Henryhouse  shale 
(Hiatus) 

Chimneyhill  limestone 

Sylvan  shale 
[  Viola  limestone 
<  Simpson  formation 
[  Arbuckle  limestone) 

Arbuckle  limestone/ 

Reagan  sandstone 


Thickness 


0-500' 
(Max)  1600' 

0-200' 
(Max.)  650' 

0-90' 
0-166' 

0-223' 

c-53' 
6o'-30o' 

1 200 '-2000' 

40oo'-6ooo' 

0-500' 


Sedimentary  rocks. — In  the  Arbuckle  Mountains,  surrounding  the 
pre-Cambrian  igneous  rocks,  and  resting  unconformably  upon  them,  is 
a  series  of  sedimentary  beds,  10,000  or  more  feet  in  thickness.  The 
maximum  for  all  the  formations  totals  over  12,000  feet.  These  sedi- 
ments belong  to  the  Paleozoic.  To  the  north,  west,  and  southwest 
lie  the  Permian  Red  Beds.  At  the  southeast  the  Cretaceous  overlaps 
and  extends  upon  the  granite,  covering  all  older  formations.  A  table 
showing  the  formations  extending  from  the  Middle  Cambrian  through 
Permian  is  given  in  Table  I.  Sedimentation  was  almost  continuous 
from  Middle  Cambrian  to  near  the  close  of  the  Mississippian,  there 
being  but  three  small  breaks  before  the  marked  one  between  the 
Mississippian  and  Pennsylvanian.  Toward  the  end  of  the  Mississip- 
pian the  area  was  uplifted,  and  the  rocks  were  folded  and  faulted. 
Then  these  folded  rocks  were  eroded  almost  to  a  peneplain  before  the 
Franks  conglomerate  of  Pennsylvanian  age  was  deposited.  A  second 
period  of  folding  and  erosion  followed,  making  the  Permian  Red  Beds 
unconformable  upon  the  edges  of  all  the  older  rocks.  While  all  the 

1  B.  F.  Wallis,  Okla.  Geol.Surv.  Bull.  23  (1915),  p.  32. 


STUDIES  IN  MINOR  FOLDS  19 

formations  from  Middle  Cambrian  to  Upper  Mississippian  were  deformed 
together,  and  all  are  involved  in  the  larger  structures,  the  minor  folds 
occur  within  the  limits  of  certain  formations.  As  illustrations  will  be 
used  only  from  the  Arbuckle  and  Simpson,  only  these  two  formations 
will  be  described. 

The  oldest  sedimentary  formation  in  the  region,  the  coarse  Reagan 
sandstone,  is  succeeded  conformably  by  the  Arbuckle  limestone.  This 
is  the  most  competent  formation  in  the  region.  It  is  heavy  bedded, 
and  has  the  great  thickness  of  4,000  to  6,000  feet.  Most  of  the  beds 
are  a  foot  or  more  in  thickness,  and  some  are  over  10  feet.  In  general 
the  texture  varies  from  fine  even  granular  to  compact,  but  some  parts  are 
coarsely  crystalline,  and  some  rather  shaly  members  occur  near  the  top. 

The  Simpson  formation  reaches  a  thickness  of  1,200  to  2,000  feet. 
The  lower  part  consists  of  sandstone  with  shales,  then  limestone  and 
more  sandstone,  and  thinly  bedded  shaly  limestones  above.  So  in 
contrast  with  the  Arbuckle  limestone,  the  Simpson  is  relatively  weak 
and  incompetent.  In  the  Wichita  Mountains  the  sedimentary  forma- 
tions have  much  the  same  characteristics  as  in  the  Arbuckles  in  so  far 
as  they  are  exposed,  but  the  Red  Beds  still  cover  all  but  the  Reagan, 
Arbuckle,  and  a  little  of  the  Viola. 

Structure  of  rocks. — As  noted  before,  all  the  Paleozoic  formations 
except  the  Pennsylvanian  and  Permian  were  deformed  together,  the 
deformation  including  intense  folding  and  faulting.  The  general  trend 
of  the  larger  folds  is  northwest-southeast,  and  they  are  several  miles  in 
width.  Upon  them  are  the  smaller  folds  of  one  or  more  orders.  On 
one  of  the  large  folds,  C.  A.  Reeds1  has  recognized  ten  smaller  longi- 
tudinal ones,  and  several  still  smaller  transverse  ones  of  a  third  order. 
In  both  groups  of  mountains  the  Arbuckle  limestone  exhibits  these 
minor  folds  of  several  orders  on  the  major  ones.  These  major  folds, 
many  of  which  have  plunging  axes,  have  been  truncated  by  erosion, 
and  the  edges  of  the  strata  in  these  truncated  folds  show  clearly  on  the 
plateaus. 

Types  of  folds. — As  indicated  above,  some  types  of  folds  are  found 
in  the  folded  mountain  areas  that  do  not  occur  in  the  eastern  lake 
region.  The  two  types  already  illustrated — the  dome,  and  the  closed 
fold — will  be  treated  more  in  detail,  and  some  plunging  folds  illustrated 
and  described. 

The  dome  shown  in  Figure  13  occurs  in  the  channel  near  the  head 
of  Falls  Creek,  where  a  good  section  has  been  exposed  by  the  stream 

1  C.  A.  Reeds,  Okla.  Geol.  Surv.  Bull.  3  (1910),  pp.  51-53. 


20 


STUDIES  IN  MINOR  FOLDS 


cutting  across  it.  It  is  a  very  close  and  conical  fold  to  be  formed  in 
a  heavy-bedded  formation,  and  shows  well  how  abruptly  parts  of  this 
thick-bedded  limestone  have  been  folded.  The  bed  at  the  left  is  4  feet 
3  inches  thick.  Another  picture  was  taken  across  the  eroded  north  end 
of  the  dome  across  the  right  foreground  in  Figure  13.  This  view  is 
given  in  Figure  14,  in  which  the  abrupt  curve  in  these  heavy  beds  is 
shown.  The  stream  has  eroded  a  deep  hole  at  the  left  from  the  crest 
of  the  fold.  This  is  the  most  abrupt  one  of  a  series  of  small  folds  found 
on  the  large  Arbuckle  anticline. 

Another  type  of  fold  in  a  different  relation  occurs  one-fourth  mile 
below  Crusher,  on  the  southeast  side  of  the  Washita  River.     Here  the 


FIG.  19. — Diagram  of  a  part  of  southwest  limb  of  Arbuckle  anticline,  showing 
folds  in  the  thin-bedded  Simpson  formation.  The  heavy  beds  at  the  left  represent 
the  Arbuckle  limestone. 

minor  folds  are  on  the  southwest  limb  of  the  same  large  Arbuckle  anti- 
cline. The  center  of  the  large  fold  and  the  inner  part  of  the  southwest 
limb  are  occupied  by  the  heavy  beds  of  the  Arbuckle  limestone,  and 
succeeding  these  toward  the  southwest  are  the  thin  beds  of  the  Simpson. 
These  relations  are  shown  in  Figure  19.  The  sharp  folds  shown  in  the 
diagram  are  in  the  thin  beds  in  the  Simpson.  The  beds  to  the  right  of 
the  fold  are  the  sandstones  of  the  Simpson,  while  the  thick  beds  at  the 
left  represent  the  Arbuckle  limestone.  This  illustrates  the  difference  in 
the  response  to  the  compressive  stresses  in  the  two  formations.  In  the 
Arbuckle  the  readjustment  has  taken  place  between  the  heavy  beds, 
while  in  the  Simpson  it  has  taken  place  across  the  thin  beds,  throwing 
these  thin  beds  into  acute  folds.  Figure  10  shows  the  central  part  of 
one  of  these  close  folds.  These  folds  are  in  the  position  on  the  large 


STUDIES  IN  MINOR  FOLDS  21 

anticline  in  which  there  is  the  maximum  of  readjustment,  for  it  is  least 
at  the  crest  of  an  anticline  and  the  trough  of  a  syncline,  and  most  at 
intermediate  points  on  the  limb.1  These  minor  folds  not  only  show  the 
difference  in  the  response  of  the  two  formations,  but  they  are  a  measure, 
in  part  at  least,  of  the  readjustments  that  have  taken  place  between 
the  beds  in  the  Arbuckle  limestone.  Leith  has  stated  succinctly  this 
relation  the  folds  in  the  weaker  formations  bear  to  the  movements 
between  the  more  resistant  ones,  as  follows: 

Rocks  within  our  field  of  observation  are  of  varied  competence.  It 
follows  then  that  in  any  folded  area  the  structures  of  the  weaker  rocks  are 
controlled  by  the  folding  of  the  stronger  beds,  and  these  tend  to  assume  the 
"parallel"  type  of  fold,  in  which  the  readjustment  is  between  the  beds  rather 
than  in  them.  This  readjustment  or  slipping  is  concentrated  in  the  interven- 
ing weaker  layers.  The  structures  of  the  weaker  layers  indicate  the  direction 
of  the  readjustment,  and  thus  something  of  the  structure  of  the  competent  beds.2 

More  common  than  the  dome  and  the  closed  fold  are  those  of-a  more 
open  type  which  generally  have  plunging  axes.  Two  broad  open  anti- 
clines with  an  intermediate  synclinal  trough  are  shown  in  Figure  20. 
They  occur  on  the  north  side  of  the  Wichita  Mountains,  where  the 
general  dip  is  northward  toward  the  left.  These  are  minor  folds  on 
a  series  of  much  larger  ones  succeeding  one  another  across  the  broad 
exposure  of  the  Arbuckle  limestone.  At  this  locality,  this  formation  has 
exceptionally  heavy  beds,  some  of  them  being  over  10  feet  in  thickness. 

A  part  of  a  more  sharply  plunging  fold  in  the  Arbuckle  Mountains  is 
shown  in  Figure  21,  in  which  the  beds  are  seen  to  curve  around  from  the 
foreground  toward  the  right.  This  plunging  anticline  is  only  one  of  a 
large  number  exposed  over  hundreds  of  acres  of  this  plateau.  The  trees 
in  the  center  of  Figure  2 1  are  on  the  sides  of  the  channel  of  Falls  Creek, 
near  its  head.  A  few  miles  to  the  north,  the  Arbuckle  limestone  is 
mineralized,  and  some  zinc  has  been  taken  from  it. 

When  it  is  realized  that  minor  folds  may  be  the  key  to  the  solution 
of  major  complex  structures,  they  are  invested  with  a  new  significance. 

Summary  of  minor  folds  in  association  with  major  folds. — From  this 
brief  consideration  of  minor  folds  associated  with  major  ones,  it  is 
concluded  that  they  are  worthy  of  careful  attention  and  study,  as  they 
may  be  an  important  part  of  a  major  structure.  They  are  particularly 
significant  when  occurring  in  the  weaker  strata  of  a  series,  as  they 
then  give  evidence  of  the  magnitude  and  nature  of  the  differential 

1  C.  R.  Van  Hise,  Jour.  GeoL,  IV  (1896),  208. 

2  C.  K.  Leith,  Structural  Geology  (1913),  p.  114. 


22 


STUDIES  IN  MINOR  FOLDS 


movements  in  the  stronger  adjacent  rocks,  and  they  may  give  a  clue 
to  the  solution  of  the  complex  major  structures. 


FIG.  20. — A  gentle  syncline  between  two  anticlines  in  very  heavy  beds  of  Arbuckle 
limestone  on  the  north  side  of  the  Wichita  Mountains. 


FIG.  21. — Edge  of  strata  in  an  anticline  plunging  to  the  left,  near  head  of  Falls 
Creek,  Arbuckle  Mountains. 

FOLDS   IN   THE    MIDST   OF   HORIZONTAL   OR   GENTLY   DIPPING   STRATA 

Location   and   area. — This  study  of  minor  folds  began  with  a  few 
small  ones  in  the  vicinity  of  Meadville,  Pennsylvania.     Part  of  these 


STUDIES  IN  MINOR  FOLDS  23 

folds  had  been  described  earlier.1  From  this  locality  the  study  was 
carried  northward  to  Lake  Erie,  thence  westward  into  Ohio  and  east- 
ward into  New  York.  Most  of  the  study  was  limited  to  a  strip  15  to 
30  miles  wide,  along  the  south  side  of  Lake  Erie,  extending  from  Cleve- 
land, Ohio,  to  Dunkirk,  New  York,  a  distance  of  140  miles.  However, 
farther  west,  most  of  the  larger  streams  between  Cleveland  and  San- 
dusky  were  traversed  for  several  miles  from  the  lake,  and  points  were 
visited  in  east  central  New  York  and  on  both  sides  of  Lake  Ontario  in 
New  York  and  Ontario.  (See  Plate  I,  general  map.) 

This  strip  bordering  the  south  shore  of  Lake  Erie  is  at  the  north 
end  of  the  broad  structural  basin  lying  between  the  Allegheny  Plateaus 
to  the  southeast  and  the  Cincinnati  Arch  on  the  west. 

There  seems  to  have  been  an  impression  that  in  this  area  in  which 
the  rocks  in  general  are  flatrlying,  no  folds  would  be  found.  White  says 
of  this  area: 

If  there  be  any  anticlinical  and  synclinal  undulations  at  all  in  Erie  and 
Crawford  counties,  they  are  so  exceedingly  flat  that  nothing  short  of  an  expen- 
sive system  of  measured  borings,  connected  by  instrumental  surveys,  would 
suffice  to  reveal  their  presence,  measure  their  force  and  determine  their  direc- 
tion; which  by  the  way  should  be  from  the  northeast  to  southwest  at  some 
angle  approximately  parallel  to  the  anticlinal  rolls  of  Clarion,  Butler  and 
Beaver  counties.2 

When  some  folds  were  found,  an  attempt  was  made  to  connect 
them  with  the  Appalachian  structure  to  the  southeast,  but  it  was  con- 
cluded that  they  could  not  be  related  to  the  larger  folds  because  their 
axes  were  variable,  and  because  they  were  not  parallel  with  those  of  the 
major  structures  to  the  southeast.3  This  study  has  brought  out  the 
fact  that  numerous  small  folds  and  faults  exist  in  this  region. 

TOPOGRAPHY   OF   THE   AREA 

This  area  bordering  the  south  side  of  Lake  Erie  is  naturally  divided 
into  two  provinces — the  Lake  Plain  and  the  Upland. 

The  Lake  Plain. — The  Lake  Plain  is  a  narrow  strip  varying  from  4  to 
6  miles  in  width.  The  elevation  of  this  plain  above  the  lake  along  its 
northern  edge  is  variable.  Northeast  of  Cleveland  there  is  a  25-foot 
bluff,  while  north  of  Geneva,  12  miles  west  of  Ashtabula,  there  is  no 
cliff.  For  most  of  the 'distance  eastward  the  cliff  varies  from  25  to 

1  Smallwood  and  Hopkins,  Bull.  Syracuse  Univ.,  4th  Ser.,  No.  i  (1903),  pp.  18-24. 

2 1.  C.  White,  Second  Geol.  Surii.  Pa.,  Kept.  Q4  (1881),  p.  45. 

3  Smallwood  and  Hopkins,  op.  cit.,  pp.  18^24;  and  I.  C.  White,  op.  tit.,  p.  45. 


24  STUDIES  IN  MINOR  FOLDS 

60  feet.  However,  at  points  northwest  of  Girard  and  north  of  North 
East,  Pennsylvania,  it  has  a  height  of  more  than  125  feet.  Along  its 
southern  margin  this  plain  rises  from  100  to  200  feet  above  the  lake. 
The  general  slope  of  the  plain  toward  the  lake  is  20  to  40  feet  per  mile, 
though  some  parts  of  it  are  very  flat,  as  in  the  area  west  of  Painesville, 
Ohio.  The  plain  is  trenched  by  several  large  streams  crossing  it,  the 
most  important  of  which  are  the  Cuyahoga,  Chagrin,  Grand,  and  Ashta- 
bula  rivers,  and  the  Conneaut,  Elk,  Walnut,  Mill,  Sixteen  Mile,  Twenty 
Mile,  Chautauqua,  and  Canadaway  creeks.  Most  of  these  streams 
cross  the  plain  through  valleys  with  steep  banks  which  frequently  are 
80  feet  or  more  in  height.  Some  of  the  streams  have  widened  their 
valleys  to  a  fourth-  or  a  half-mile,  and  a  few  have  locally  widened  them 
still  more.  Along  the  channel  numerous  terraces  occur  at  various  inter- 
vals above  the  flood  plains.  Between  the  major  streams  numerous 
small  ones  cross  the  plain.  A  few  of  these  have  deep  channels,  but 
most  of  them  flow  through  slight  depressions. 

The  Upland — The  northern  part  of  this  Upland  forms  the  divide 
between  the  streams  tributary  to  Lake  Erie  and  those  flowing  south. 
From  Cleveland  east  to  Girard  the  divide  is  about  25  miles  south  of 
the  lake  shore.  Eastward  from  Girard  it  is  less  than  10  miles  from  the 
lake.  At  the  inner  edge  of  the  Lake  Plain  there  generally  is  an  abrupt 
slope  in  the  form  of  a  lake  cliff  marking  a  former  higher  level  of  the 
lake.  At  the  west  the  divide  usually  is  flat,  with  elevations  reaching 
above  1,300  feet  (Lake  Erie  is  573'  A.T.).  Toward  the  east  the  divide 
rises  to  over  1,600  feet,  or  about  900  feet  above  the  lake,  though 
some  of  the  hills  in  the  Clymer  quadrangle  have  elevations  above 
i, 800  feet.  The  rise  from  the  Lake  Plain  is  less  marked  at  the  west 
than  in  the  east.  Five  miles  west  of  Westfield,  New  York,  the  rise  is 
500  feet  in  three-fourths  of  a  mile. 

The  Upland  is  very  prematurely  dissected,  or  in  a  youthful  stage 
of  erosion.  The  larger  streams  tributary  to  the  lake  have  trenched 
their  post-glacial  valleys  through  glacial  till  deeply  into  the  bedrock. 
The  banks  along  many  of  the  streams  rise  abruptly  80  or  100  feet  above 
the  valley  floor,  and  in  the  gulf  south  of  Westfield  the  banks  rise  400  feet 
above  the  stream.  As  in  the  Lake  Plain,  so  in  the  Upland,  terraces 
with  varying  intervals  occur  in  these  valleys.  The  large  streams  form- 
ing a  part  of  the  southward  drainage  flow  for  the  most  part  through 
broad,  flat  valleys,  from  which  hills  rise  by  several  easy  stages  to  heights 
of  from  100  to  500  feet.  Locally,  where  streams  are  impinging  against 
the  sides  of  old  valleys,  and  in  a  few  places  where  there  is  great  inequality 


STUDIES  IN  MINOR  FOLDS 


in  hardness  of  rocks,  as  at  Thompson's  ledge,  twelve  miles  southeast  of 
Painesville,  Ohio,  steep  slopes  exist.  Some  of  the  small  tributaries  to 
these  larger  streams  have  cut  deep  valleys  into  hillsides,  exposing  thick 
sections  of  bedrock. 

TABLE  II 

SHOWING  PENNSYLVANIAN  AND  MISSISSIPPIAN  FORMATIONS  FOR  PENNSYLVANIA, 
AND   DEVONIAN,    SILURIAN,    AND    ORDOVICIAN   FOR   NEW   YORK 


(After  Clarke  and  Schuchert,1  and  White2) 


System 

Pennsylvanian 


Mississippian 


Devonian 


Formation 

f  Sharon  or  Olean 
\     conglomerate 

Shenango  beds 
Meadville  beds 
Sharps ville  sandstone 
Orangeville  shale 
Cussewago  beds 

Riceville  shale 

Chemung  beds 
Portage  beds 
Genesee  shale 
Tully  limestone 

Hamilton  beds 
Marcellus  shale 
Onondaga  limestone 
Schoharie  grit 
Esopus  grit 

Oriskany  beds 
Kingston  beds 
Becraft  limestone 
New  Scotland  beds 
Coeymans  limestone 


System 


Silurian 


Formation 

Manlius  limestone 
Rondout  waterlime 
Salina  beds 

Guelph  dolomite 
Lockport  limestone 
Rochester  shale 
Clinton  beds 

Medina  sandstone 
i  Oneida  conglomerate 

Richmond  beds 
Lorraine  beds 
Utica  shale 


Ordovician  < 


Trenton  limestone 
Black  River  limestone 
Lowville  limestone 


Chazy  limestone 
Beekmantown  limestone 


STRATIGRAPHY 

In  the  region  along  Lake  Erie  the  exposed  rocks  extend  in  age  from 
Upper  Devonian  to  Lower  Pennsylvanian.     However,  as  other  areas  of 

1 J.  M.  Clarke  and  C.  Schuchert,  Science,  New  Ser.,  X  (1899),  876. 
2 1.  C.  White,  Second  Geol.  Surv.  Pa.,  Rept.  Q<  (1881),  pp.  55,  56. 


26  STUDIES  IN  MINOR  FOLDS 

older  rocks  were  visited  farther  east  and  northeast,  a  few  of  the  older 
formations  will  be  characterized  briefly.  To  indicate  their  relative 
position,  the  succession  is  shown  in  Table  II.  In  this  table  the  Penn- 
sylvanian  and  Mississippian  are  for  northwestern  Pennsylvania,  and 
the  Devonian,  Silurian,  and  Ordovician  for  New  York. 

ORDOVICIAN  FORMATIONS 

Beekmantown  limestone. — This  formation  and  the  pre-Cambrian 
syenite  on  which  it  rests  in  all  the  exposure  of  the  latter  in  the  quad- 
rangle, were  seen  near  the  west  edge  of  the  Little  Falls  quadrangle  at 
Middleville,  8  miles  north  of  Herkimer,  New  York.  About  200  feet  of 
Beekmantown  are  exposed  at  this  locality.1  The  Beekmantown  is  a 
gray,  sandy  dolomitic  limestone.  The  thickness  of  the  beds  varies 
from  3  inches  to  2  feet.  Some  very  sandy  beds  4  to  12  inches  in  thick- 
ness were  observed  in  the  ravine  north  of  Middleville.  Some  low  open 
folds  occur  in  this  formation  similar  to  those  in  the  following  one. 

Lowville  limestone. — The  Chazy  formation  being  absent  in  this  Little 
Falls  area,  there  must  be  disconformity  between  the  Beekmantown  and 
the  Lowville.2  The  Lowville  is  a  medium  to  thin-bedded  pure  gray 
limestone,  which  near  Middleville  has  a  thickness  of  only  about  20  feet. 
Gushing  shows  two  good  exposures  of  it  in  Plates  5  and  6,  in  Bulletin 
77  of  the  New  York  State  Museum  series.  In  the  latter  of  these  two 
plates  the  low  folds  are  well  shown. 

Trenton  limestone. — The  thin  formation  of  limestone  and  shale 
above  the  Lowville — the  Black  River — was  not  exposed  at  the  two  areas 
visited  in  the  Remsen  quadrangle.  The  Trenton  was  seen  at  Graves- 
ville  near  the  southern  edge  of  the  Remsen  quadrangle,  20  miles  north- 
west of  Herkimer,  and  at  Prospect,  4  miles  northwest  of  Gravesville. 
"  In  general  this  formation  may  be  said  to  be  made  up  of  thin  bedded, 
dark  bluish  compact  limestones  with  thin  shaly  partings."3  The  Tren- 
ton limestone  is  very  fossiliferous. 

The  formations  in  the  Upper  Ordovician  will  not  be  mentioned 
except  to  note  that  the  next  formation,  the  Queenston  shale,  may  in 
part  be  equivalent  to  the  Richmond.4 

Queenston  shale. — The  Queenston  shale  is  exposed  at  the  lower  end 
of  the  Niagara  Gorge  at  Queenston,  Ontario,  whence  it  derives  its 

1 H.  P.  Gushing,  New  York  State  Mus.  Bull  77,  Geol.  6  (1905),  p.  28. 

2  H.  P.  Gushing,  ibid.,  pp.  27-30. 

3  W.  J.  Miller,  New  York  State  Mus.  Butt.  126  (1909),  p.  17. 

4  E.  M.  Kindle  and  F.  B.  Taylor,  Niagara  Folio,  No.  190  (1913),  p.  6. 


STUDIES  IN  MINOR  FOLDS 


27 


name.  It  is  exposed  eastward  along  the  south  shore  of  Ontario  across 
the  Niagara  quadrangle,  and  in  the  valleys  of  the  streams  flowing  into 
the  lake.  It  is  particularly  well  exposed  in  the  gorge  of  Eighteen  Mile 
Creek,  two  miles  south  of  Olcott,  New  York.  The  same  type  of  for- 
mation, with  colors  and  physical  characteristics  the  same,  is  exposed 
on  the  north  shore  of  Lake  Ontario  to  the  east  of  Burlington,  both  along 
the  shore  and  in  valleys  of  streams  tributary  to  the  lake.  The  Canadian 
geological  map  shows  that  the  Silurian  extends  around  the  west  end  of 
Lake  Ontario  and  on  the  north  side  well  up  toward  Toronto.1  The 
Queenston  formation  consists  chiefly  of  friable  shale  with  some  interca- 
lated thin  sandstone  beds.  The  predominating  color  is  red,  but  beds 
of  green  and  gray  shales  and  sandstone  occur,  interspersed  through  the 
red  shales.  The  total  thickness,  determined  from  deep  wells,  is  1,200 
feet,  only  300  feet  of  which  are  exposed.2 

Passing  over  the  rest  of  the  Silurian  formations  and  the  Lower  and 
Middle  Devonian,  the  Portage  group  in  the  Upper  Devonian  will  next 
be  considered.  (See  basal  part  in  center  of  Table  III.) 

TABLE  III 

UPPER    DEVONIAN    AND    LOWER    MISSISSIPPIAN    FORMATIONS    FOR    OHIO,    PENN- 
SYLVANIA,  AND   NEW  YORK 


System 


Lower 
Mississippian 


Ohio' 

Sunbury  shale 
Berea  grit 
Bedford  shale 
Cleveland  shale 


Pennsylvania* 

Orangeville  shale 
Corry  sandstone 


New  York* 

Knapp  formation 
Cussewago  sandstone 
Riceville  shale  Oswayo  formation 


Upper 


Devonian 


Chemung 


Chagrin  formation    Girard  shale 


Huron  shale  Portage6 

Atlas  of  Canada,  No.  5,  "Geology,  East  Sheet." 


Cattaraugus 
Chemung 


Portage  beds? 


2  Kindle  and  Taylor,  op.  cit.,  p.  5. 

3  C.  S.  Prosser,  Geol.  Surv.  Ohio  Butt.  7,  4th  Ser.  (1905),  p.  4. 

* 1.  C.  White,  Second  Geol.  Surv.  Pa.,  Rept.  Q<  (1881),  pp.  117-20. 

s  Elkland-Tioga  Folio  (1903),  p.  5;  Warren  Folio  (1910),  p.  3;  C.  Schuchert, 
Bull.  Geol.  Soc.  Amer.,  XX  (1908),  548;  L.  C.  Glenn,  N.Y.  Stale  Mus.  Bull.  69  (1903), 
pp.  967-95. 

6  J.  M.  Clarke,  N.Y.  State  Mus.  Bull.  69  (1903),  p.  853. 

7  D.  D.  Luther,  N.Y.  State  Mus.  Bull.  69  (1903),  pp.  1000-1029. 


28  STUDIES  IN  MINOR  FOLDS 

UPPER   DEVONIAN   FORMATIONS 

Portage  group. — White  gives  the  name  of  Portage  to  the  oldest  rocks 
exposed  in  northwestern  Pennsylvania.  Coming  from  beneath  the  lake 
2  miles  east  of  the  Ohio  state  line,  they  rise  until  475  feet  are  exposed 
at  the  New  York  state  line.1  These  rocks  consist  of  gray  shales  and 
flaggy  sandstones.  The  layers  of  sandstone  usually  are  12  inches  or 
less  in  thickness,  occasionally  2  feet.  White  follows  Hall's  earlier 
identification  of  these  rocks  as  Portage.2  Clarke,  however,  says  there 
is  no  Portage  in  northwestern  Pennsylvania.3 

The  Portage  group  has  been  restudied  by  Clarke  and  Luther4  in  its 
type  section  at  Portage  on  the  Genesee  River  and  in  its  general  expo- 
sures, and  they  have  made  a  detailed  geological  map  for  the  group  in 
western  New  York,  which  shows  the  rocks  of  this  group  extending  from 
Seneca  Lake  in  a  strip  with  irregular  borders  to  the  shore  of  Lake  Erie. 
According  to  this  map  the  most  westward  exposure  of  the  Portage 
extends  a  little  west  of  Westfield,  New  York.  As  there  is  a  general 
dip  of  the  formations  here  toward  the  southwest,  only  a  marked  anti- 
cline or  a  fault  would  expose  the  Portage  again  in  Pennsylvania. 

The  Portage  group,  as  recently  described,  consists  of  nine  formations 
shown  in  the  following  table,  in  which  the  thickness  of  each  formation 
and  the  total  thickness  are  given.5 

TABLE  IV 

PORTAGE   GROUP 

(After  Clarke  and  Luther) 

Formations  Thickness 

1.  Passage  shales 3' 

2.  Middlesex  black  shale 32' 

3.  Cashaqua  shale 165' 

4.  Rhinestreet  black  shale 53' 

5.  Hatch  shale 203' 

6.  Grimes  sandstone 25' 

7.  Gardeau  shales  and  flags 372' 

8.  Portage  sandstones ~. 187' 

9.  Wiscony  shale 167' 

Total , 1207' 

1 1.  C.  White,  Second  GeoL  Surv.  Pa.,  Rept.  Q*  (1881),  pp.  119-20. 

2  J.  Hall,  Nat.  Hist.  N.Y.  4th  Dist.,  Part  IV  (1843),  P-  238. 

3  J.  M.  Clarke,  N.Y.  State  Mus.  Bull.  6g,  Paleon.  9  (1902),  p.  853. 

«J.  M.  Clarke,  ibid.,  pp.  1000-1029,  and  Geol.  Map;    also  J.  M.  Clarke  and 
D.  D.  Luther,  N.Y.  State  Mus.  Bull.  118,  Paleon.  18  (1908),  pp.  1-69. 
5  Clarke  and  Luther,  ibid.,  p.  1010. 


STUDIES  IN  MINOR  FOLDS  29 

This  total  thickness  is  a  little  above  Hall's  earlier  estimate  of  over 
1,000  feet.1  The  foregoing  table  shows  the  general  character  of  the 
Portage  in  New  York.  If  the  northwest  dip  continues  constant,  so 
that  none  of  the  Portage  group  is  exposed  along  the  lake  in  Erie  County, 
Pennsylvania,  the  rocks  there  formerly  called  " Portage"  must 
be  younger.  Dr.  Clarke  has  reached  this  conclusion,  for  he  says:  "The 
'Portage'  and  'Girard  Shales'  of  Erie  County,  Pennsylvania,  are  later 
than  Portage  time."2  Also,  Chemung  brachiopods  have  been  collected 
near  the  lake  north  of  North  East,  Pennsylvania,  in  what  was  con- 
sidered the  lower  part  of  the  "Portage"  for  that  locality.3 

Huron  shale. — The  position  of  the  Huron  shale  in  northeastern 
Ohio  is  in  question.  The  name  was  given  to  the  black  bituminous 
shales  exposed  along  the  Huron  River.  Prosser  took  the  position  that 
the  Huron  west  of  Cleveland  is  at  least  in  part  synchronous  with  the 
Chagrin  to  the  east.4  If  the  two  are  in  contact  at  all,  the  darker  lower 
shales  may  then  be  called  Huron. 

Girard  shales. — The  Girard  shales  appear  above  the  lake  a  short 
distance  east  of  the  Ohio  state  line,  and  the  basal  beds  rise  to  475  feet 
above  it  at  the  New  York  state  line.  They  are  gray  and  grayish-blue 
shales  containing  a  few  thin  beds  of  sandstone,  and  have  a  thickness  in 
Pennsylvania  of  225  feet.5  They  are  very  friable  and  easily  eroded. 
In  some  localities  they  contain  large  calcareous  concretionary  lenses, 
while  in  others,  cone-in-cone  is  common.  The  relation  of  the  Girard 
shales  to  the  Chagrin  is  seen  in  the  following  statement:  "The  Girard 
shales  lithologically  are  very  similar  to  the  lower  part  of  the  Chagrin 
formation  as  seen  in  northeastern  Ohio,  of  which  they  are  the  eastern 
continuation.6  They  now  are  thought  to  be  Chemung  in  age.7  They 
contain  few  fossils. 

Chagrin  formation. — The  Chagrin,  or  Erie,  shales  are  soft  bluish 
gray,  containing  a  few  thin  sandstone  beds  and  locally  calcareous  beds. 
The  upper  part  of  the  Chagrin  is  considered  Chemung.8  As  just  noted, 
the  lower  part  is  equivalent  to  the  Girard  shales.  The  Chagrin 

1  J.  Hall,  op.  cit.,  p.  238. 

» J.  M.  Clarke,  Bull.  Geol.  Soc.  Amer.,  XIV  (1902),  536. 

3  D.  D.  Luther,  N.Y.  State  Mus.  Bull.  6p,  Paleon.  9  (1903),  p.  1028. 

4  C.  S.  Prosser,  Geol.  Surv.  Ohio  Bull.  75,  4th  Ser.  (1912),  pp.  515,  519. 
s  I.  C.  White,  Second  Geol.  Surv.  Pa.,  Rept.  Q"  (1881),  pp.  118,  119. 

6  C.  S.  Prosser,  Geol.  Surv.  Ohio  Bull.  15,  4th  Ser.  (1912),  p.  451. 

7  C.  S.  Prosser,  ibid.,  p.  451. 

8  C.  S.  Prosser,  op.  cit.,  pp.  462-64. 


30  STUDIES  IN  MINOR  FOLDS 

formation  is  widely  distributed  in  northeastern  Ohio,  and  extensive  expo- 
sures of  it  may  be  seen  in  nearly  all  the  valleys  of  the  rivers  and  larger 
creeks. 

Chemung  formation. — The  Chemung  of  northwestern  Pennsylvania 
is  described  as  composed  of  alternate  groups  of  shale  and  sandstone, 
with  a  thickness  of  325  feet.1  If  the  rocks  called  "Girard  shales"  and 
" Portage"  are  also  Chemung,  the  total  thickness  would  be  1,025  feet. 
As  noted  above,  the  Chemung  is  continued  into  Ohio  as  the  upper  part 
of  the  Chagrin  formation.  Hall  says  of  the  Chemung  that  "this  group 
consists  of  a  highly  fossiliferous  series  of  shales  and  thin-bedded  sand- 
stones, sometimes  in  well-defined  and  distinct  courses,  and  an  infinite 
variety  resulting  from  the  admixture  of  the  two  ingredients."2  The 
colors  are  green,  gray,  and  black.  The  formation  becomes  pebbly  and 
conglomeratic  toward  the  top.  The  Chemung  has  a  thickness  of 
1,120  feet  in  the  Warren  quadrangle.3  This  quadrangle  is  in  the  northern 
part  of  Warren  County,  Pennsylvania,  which  is  east  of  Erie  County  in 
the  same  state,  and  south  of  Chautauqua,  the  most  western  county  of 
New  York. 

Cleveland  shale. — In  northeastern  Ohio  the  uppermost  formation 
recognized  in  the  Devonian  is  the  Cleveland  shale.4  It  is  a  carbo- 
naceous shale  of  brownish-black  color  and  homogeneous  texture.  In 
thickness  it  varies  from  30  to  200  feet.5  East  of  Cleveland  the  forma- 
tion decreases  in  thickness  and  disappears  in  Trumbull  and  Ashtabula 
counties.6  Edward  Orton  includes  the  Cleveland,  Erie  (Chagrin), 
and  Huron  shale  all  under  the  Ohio  shale.7 

Cattaraugus  formation. — In  southwestern  New  York  and  in  north- 
western Pennsylvania,  the  Cattaraugus  is  the  name  given  to  a  thick 
formation  of  Upper  Devonian  age  next  above  the  Chemung.8  In  the 
Gaines  quadrangle  in  northern  Pennsylvania  this  formation  consists  of 
red,  gray,  and  green  shales  alternating  with  brown  and  green  sand- 
stones. Northward,  in  southern  New  York,  several  conglomerate  mem- 

1 1.  C.  White,  op.  cit.  (1881),  p.  117. 

>  J.  Hall,  Nat.  Hist.  N.Y.  4th  Dist.,  Part  IV  (1843),  P-  252. 

3  Warren  Folio,  No.  172  (1910),  p.  3. 

*  C.  S.  Prosser,  Geol.  Surv.  Ohio  Bull..  15,  4th  Ser.  (1912),  pp.  16-21. 

s  E.  Orton,  Geol.  Surv.  Ohio,  Econ.  Geol.,  VI  (1888),  26. 

6  C.  S.  Prosser,  Geol.  Surv.  Ohio  Bull.  15,  4th  Ser.  (1912)  pp.  509-14. 

7  E.  Orton,  Geol.  Surv.  Ohio,  Econ.  Geol.,  VI  (1888),  23. 

8  L.  C.  Glenn,  N.Y.  State  Mus.  Bull.  69,  Paleon.  9  (1903),  pp.  971-78;  and  Gaines 
Folio,  No.  92  (1903),  columnar  section  at  back. 


STUDIES  IN  MINOR  FOLDS  31 

bers  are  recognized  in  the  midst  of  the  formation.     In  the  Gaines  area 
it  is  about  500  feet  in  thickness. 

DEVONO-CARBONIFEROUS    FORMATIONS 

Under  this  head  are  classed  several  transitional  formations  which 
have  not  been  definitely  assigned  either  to  the  Devonian  or  Mississippian. 
Two  will  be  noted  here,  the  Riceville  shale  and  the  Oswayo  formation. 

Riceville  shale.- — In  Crawford  County,  Pennsylvania,  the  Riceville 
shale  consists  of  80  feet  of  grayish-blue  shales  and  shaly  sandstone. 
Correlation  with  parts  of  Cleveland  and  Bedford  shales  of  Ohio  have 
been  suggested.1  The  Riceville  contains  many  fossils  common  in  the 
Chemung. 

Oswayo  formation. — In  northern  Pennsylvania  a  series  of  shales  and 
sandstones  about  1,000  feet  thick  has  been  assigned  to  this  formation, 
and  it  has  been  classed  as  Devono-Carboniferous  in  age.2  In  south- 
western New  York  it  is  classed  with  the  Carboniferous  formations  by 
Glenn.3 

MISSISSIPPIAN   FORMATION 

Bedford  shale. — Of  the  Mississippian  formations  given  in  Tables  II 
and  III,  folds  were  found  only  in  the  Bedford  shale,  so  only  that  one 
will  be  described.  It  is  placed  at  the  base  of  the  Mississippian  forma- 
tions of  northeastern  Ohio,  and  succeeds  the  Cleveland  shale,  being  suc- 
ceeded by  the  Berea  grit,  that  being  correlated  with  the  Cussewago 
and  Corry  formations  of  Pennsylvania.4  The  Bedford  formation  is 
extremely  variable  in  thickness,  for  its  top  surface  is  very  irregular, 
marking  an  unconformity  between  it  and  the  Berea.  It  consists  chiefly 
of  bluish-gray  and  chocolate-colored  shales  with  a  varying  amount  of 
sandstone  interspersed.  In  its  type  locality  it  has  a  thickness  of  88  feet.5 

PENNSYLVANIAN  FORMATION 

Sharon  or  Olean  conglomerate. — The  youngest  formation  in  the  region 
under  consideration  is  the  Sharon  or  Olean  conglomerate.  It  has  a 
marked  unconformity  at  the  base,  and  is  found  only  on  the  tops  of  the 
highest  hills  back  a  considerable  distance  from  the  lake,  in  Ohio,  Penn- 
sylvania, and  New  York.  It  is  a  coarse  conglomerate  with  white 

1 1.  C.  White,  Second  Geol.  Surv.  Pa.,  Rept.  Q<  (1881),  p.  97- 

3  Gaines  Folio,  No.  92  (1903),  p.  2. 

3  L.  C.  Glenn,  op.  tit.,  p.  978. 

<  C.  S.  Prosser,  Geol.  Surv.  Ohio  Bull.  15,  4th  Ser.  (1912),  pp.  352,  511. 

s  C.  S.  Prosser,  ibid.,  p.  87. 


32  STUDIES  IN  MINOR  FOLDS 

quartz  pebbles  generally  about  one-half  to  three-fourths  of  an  inch  in 
diameter.  Large  parts  of  it  commonly  are  strongly  cross-bedded.  At 
Thompson's  Ledge  in  northern  Ohio,  it  has  a  thickness  of  80  feet;1 
northeast  of  Meadville,  Pennsylvania,  40  feet;  and  in  the  Gaines  quad- 
rangle, in  north-central  Pennsylvania,  60  to  100  feet.2  No  indurated 
rocks  younger  than  those  of  early  Pennsylvanian  age  have  been  found 
in  this  area. 

QUATERNARY   DEPOSITS 

Pleistocene. — The  deposits  of  Quaternary  age  consist  chiefly  of 
glacial  till,  sand,  and  gravel.  The  glacial  drift  is  very  irregularly  dis- 
tributed. In  general  it  is  thinnest  on  the  hilltops  and  thickest  in  the 
valleys,  varying  from  nothing  on  the  former  to  nearly  500  feet  in  the 
latter.  The  deposits  of  the  ground  moraine  are  very  irregular  in  thick- 
ness, but  there  is  still  greater  irregularity  in  the  broad  complex  terminal 
moraines.  Locally,  extensive  deposits  of  gravel  and  sand  have  resulted 
from  glacio-fluvial  work  in  the  form  of  kames  and  kame  terraces. 

Post-glacial. — Post-glacial  deposits  have  been  formed  in  lakes  and  by 
streams.  In  small  lakes  some  peat  and  much  marl  have  been  deposited, 
while  streams  have  made  deposits  in  the  form  of  alluvial  fans,  flood 
plains,  and  deltas. 

GEOLOGIC  HISTORY 

As  noted  above,  the  oldest  rocks  exposed  in  the  specific  area  under 
consideration  are  of  Upper  Devonian  age.  However,  the  deep  well  at 
Presque  Isle,  Erie,  Pennsylvania,  at  a  depth  of  4,450  feet  is  thought  to 
have  penetrated  170  feet  of  the  Trenton  limestone,  and  the  general 
formations  of  the  New  York  section  intervening  between  the  Trenton 
and  the  Chemung  are  represented.3  Marine  conditions  seem  to  have 
been  dominant  in  the  area,  from  early  Paleozoic  until  toward  the  close 
of  the  Mississippian.  In  the  earlier  periods  limestone  predominated; 
toward  the  close,  clastic  formations.  All  older  formations  are  con- 
cealed beneath  Upper  Devonian.  The  formations  of  this  epoch  indicate 
shallow  marine  deposition  with  fine  silt  as  the  chief  sediment,  though 
alternating  rather  frequently  with  sand. 

There  seems  to  have  been  no  break  in  sedimentation  at  the  close  of 
the  period,  and  no  good  line  of  demarcation  has  been  drawn  between 
Devonian  and  Mississippian  rocks.  Marine  deposition  continued 

1  C.  S.  Prosser,  Geol.  Surv.  Ohio  Bull.  15,  4th  Ser.  (1912),  pp.  286-88. 

2  Gaines  Folio,  No.  92  (1903),  columnar  section  in  back. 

3  C.  S.  Prosser,  Geol.  Surv.  Ohio  Bull.  75,  4th  Ser.  (1912),  pp.  412-22. 


STUDIES  IN  MINOR  FOLDS  33 

through  a  large  part  of  the  Mississippian  period,  with  clastic  materials 
greatly  predominating.  Toward  the  close  of  the  latter  period  the  area 
was  elevated,  and  suffered  erosion  before  the  Pennyslvanian  rocks  were 
deposited.  After  this  erosion  interval  the  region  was  depressed,  and  a 
coarse  conglomerate  with  white  quartz  pebbles  spread  widely  over  the 
area.  Above  this  conglomerate  shales  and  coal  were  deposited,  but 
they  have  been  completely  removed  by  erosion  from  most  of  the  area. 
If  Permian  or  younger  rocks  ever  were  deposited,  all  evidences  of  their 
presence  have  been  carried  away.  It  is  thought  then  that  this  area  has 
been  above  the  sea  ever  since  a  time  near  the  close  of  the  Paleozoic. 

PHYSIOGRAPHIC   HISTORY 

Since  the  Paleozoic,  in  the  vast  periods  of  erosion  which  followed, 
the  history  of  this  area  doubtless  closely  paralleled  that  of  southwestern 
Pennsylvania.1  In  the  latter  region  erosion  is  thought  to  have  reduced 
the  land  to  a  peneplain  before  the  close  of  the  Cretaceous,  and  this 
first  great  base-level  is  called  the  Schooley  Peneplain.  Succeeding  uplift 
initiated  a  second  cycle  of  erosion  which  nearly  obliterated  the  former 
plain,  developing  the  Harrisburg  as  the  second  peneplain  in  early  Terti- 
ary time.  After  subsequent  uplift  and  erosion  a  third  less  complete 
peneplain — the  Worthington — was  developed  toward  the  close  of  Terti- 
ary time.  A  series  of  straths  and  terraces  below  the  latest  pene- 
plain is  taken  to  indicate  still  later  periodic  elevations  of  the  region. 
The  deformation  of  the  Harrisburg  or  late  Tertiary  peneplain  has  been 
worked  out  in  considerable  detail  by  M.  R.  Campbell.  He  finds  it  has 
a  domelike  uplift,  so  that  it  is  1,600  feet  higher  in  northern  Pennsyl- 
vania and  southern  New  York  than  in  southeastern  Pennsylvania.  (See 
Plate  III.)2  Doubtless  as  many  peneplains  were  developed  in  north- 
western Pennsylvania  as  in  the  southwestern  part  of  the  state,  but 
some  of  the  evidences  of  them  have  been  obliterated  by  the  heavy 
deposits  of  glacial  drift  in  the  northern  region. 

The  tops  of  the  higher  hills  easily  are  recognized  as  remnants  of  a 
peneplain.  Below  these,  broad  flat  areas  of  great  extent  seem  to  rep- 
resent a  second  less  complete  plain.  Below  this  broad  plain,  terraces 
of  varying  width  can  be  recognized,  though  they  are  materially  modified 
by  glacial  deposits.  During  the  last  period  of  erosion  preceding  glacia- 
tion,  the  valleys  were  cut  from  800  to  1,000  feet  below  the  hilltops. 
Accordingly,  when  the  continental  glaciers  invaded  this  area,  it  was  one 

1  R.  W.  Stone,  Kept.  Top.  and  Geol.  Surv.  Com.  Pa.  (1906-8),  pp.  120-22. 

2  M.  R.  Campbell,  Bull.  Geol.  Soc.  Amer.,  XIV  (1903),  277-96. 


34  STUDIES  IN  MINOR  FOLDS 

of  considerable  relief.  It  was  covered  by  that  part  of  the  glacier  called 
the  Grand  River  Glacial  Lobe.1  Glaciers  had  a  marked  effect  on  the 
topography  of  the  area.  While  glacial  erosion  seems  to  have  been 
relatively  unimportant,  glacial  deposition  and  drainage  changes  were  of 
great  importance.  Evidences  of  only  two  glacial  epochs  in  this  area 
have  been  found.2 

Glacial  erosion. — At  the  quarry  i  mile  northeast  of  Meadville,  Penn- 
sylvania, planation,  grooving,  and  striation  resulted  from  erosion,  but 
the  glacier  did  not  erode  the  rocks  deeply,  for  evidences  of  former 
weathered  surfaces  exist  below  the  plane  cut  by  the  ice.  Doubtless  the 
tops  of  the  hills  were  not  lowered  materially  by  glacial  erosion,  but 
were  only  smoothed  and  rounded  in  contour  somewhat  by  its  action. 

Glacial  deposition. — Glacial  deposition  did  affect  the  topography 
very  materially.  Terminal  moraines  with  accessory  kames,  kame 
terraces,  outwash  plains,  and  ground  moraines  with  drumlins  were 
formed.  Some  of  the  old  valleys  were  filled  in  with  much  drift,  200  to 
300  feet  of  drift  being  common,  and  nearly  500  feet  being  reached  near 
Meadville,  Pennsylvania.3  In  the  moraines  the  drift  was  deposited  in 
rounded  hills  both  in  valleys  and  on  uplands  alike. 

Drainage  changes. — The  effect  of  glaciation  on  the  drainage  systems 
of  this  area  was  very  marked.4  Several  large  northward-flowing  sys- 
tems were  practically  obliterated,  and  their  drainage  areas  added  to 
systems  of  the  southward-flowing  streams.  There  was  then  a  marked 
shifting  of  the  divide  northward.  Owing  to  conditions  near  the  close 
of  the  glacial  period,  several  of  the  northward  flowing  streams  reach  the 
lake  by  very  peculiar  courses.  As  the  ice  receded  from  the  area  toward 
the  northeast,  drainage  was  established  westward  along  its  southern 
margin,  after  it  receded  north  of  the  divide.  The  southern  margin 
remained  constant  at  a  number  of  places  for  a  sufficient  length  of  time 
for  channels  to  be  developed  parallel  with  it.  As  a  result  several 
streams  run  parallel  with  the  lake  shore  for  a  considerable  part  of  their 
course.  Another  condition  favoring  this  parallelism  is  the  trend  of  the 
morainic  deposits,  which  are  about  parallel  with  the  lake  shore.  Because 
of  these  deposits  some  of  the  streams  were  deflected  westward  on  the 
south  side  of  them.  Examples  of  this  type  of  course  are  Twenty  Mile, 
Walnut,  Elk,  and  Conneaut  creeks,  and  Ashtabula  and  Grand  rivers. 
Thus  the  headwaters  of  the  stream  in  Gage  Gulf  are  but  3  miles  from 

1  F.  Leverett,  U.S.G.S.  Mono.  41  (1902),  Plate  15. 

2  F.  Leverett,  ibid.,  pp.  272-74,  and  Plate  15. 

*  F.  Leverett,  ibid.,  p.  458.  4  F.  Leverett,  ibid.,  pp.  128-44. 


STUDIES  IN  MINOR  FOLDS  35 

the  lake,  but  it  flows  in  a  westerly  direction  for  9  miles,  then  3  miles  to 
the  lake.  From  the  abrupt  turn  at  Conneaut  Creek  north  of  Albion  it 
is  but  6  miles  to  the  lake,  but  from  that  point  it  goes  20  miles  west- 
ward and  then  over  9  miles  northeastward  to  the  lake.  The  Grand 
River  also  runs  parallel  with  the  lake  for  over  20  miles  within  8  miles 
of  the  shore. 

Glacio-Lacustrine  substage. — As  the  ice  receded  from  the  lake  basin 
it  was  occupied  by  water  standing  at  very  much  higher  levels  for  a 
series  of  stages.  To  these  various  stages  the  names  of  Maumee,  Whittle- 
sey,  Warren,  and  Dana  were  given.  At  the  Whittlesey  stage  the  water 
was  211  feet  above  the  present  level  of  Lake  Erie  at  the  New  York  state 
line.1  Besides  these  higher  lake  stages  there  were  numerous  small  ice- 
front  lakes  in  northwestern  New  York  and  Pennsylvania.2 

Post-glacial  changes. — Since  the  glaciers  receded,  the  streams  of  this 
area  have  been  active.  While  a  few  of  them  seem  to  have  accom- 
plished little,  most  of  them  have  cut  their  channels  through  the  drift 
and  into  the  bedrock  beneath.  Many  of  these  channels  are  80  to 
100  feet  in  depth,  while  the  one  south  of  Westfield,  New  York,  is  over 
400  feet  in  depth.  In  this  down-cutting  process,  numerous  terraces 
have  been  left  marking  the  old  high-stream  levels.  As  noted  above, 
stream  deposits  have  been  made  in  the  form  of  alluvial  fans,  alluvial 
plains,  and  deltas. 

Similarly,  Lake  Erie  has  been  actively  at  work  undercutting  the 
cliffs  along  its  southern  margin,  causing  the  shore  to  recede  southward. 
Sediments  derived  by  shore  erosion  and  by  transportation  of  streams 
have  been  deposited  along  the  beach  in  bars  or  hooks,  or  carried  to  the 
deeper  parts  of  the  lake  basin. 

STRUCTURE    OF   THE   ROCKS 

General  structure. — The  rocks  of  the  area  in  general  appear  to  be 
flat-lying,  although  the  distribution  of  formations  on  the  geologic  map 
shows  a  belted  arrangement  characteristic  in  regions  with  monoclinal 
dip.  The  oldest  rocks  are  exposed  along  the  lake,  and  successively 
younger  ones  toward  the  south.  The  dip  of  the  rocks  in  northwestern 
Pennsylvania  has  been  figured  to  be  about  20  feet  per  mile  southward 
and  10  feet  per  mile  westward.3  The  amount  of  dip,  however,  is  not 
constant,  but  increases  toward  the  northeast. 

XH.  L.  Fairchild,  N.Y.  State  Mus.  Bull.  106  (1907),  pp.  42-44. 

2  H.  L.  Fairchild,  ibid.,  pp.  33-41. 

3  J.  P.  Lesley,  Second  Geol.  Sun.  Pa.,  Rept.  Q4  (1881),  pp.  45-49. 


36  STUDIES  IN  MINOR  FOLDS 

Local  structures. — In  this  general  area  of  very  gently  dipping  rocks, 
numerous  irregularities  occur  in  the  form  of  small  folds  and  faults.  The 
faults  are  all  thrust  faults,  but  among  the  folds,  besides  the  specific 
types  before  mentioned,  several  general  types  will  be  considered. 

GENERAL   TYPES   OF   FOLDS 

Intra-formational  folds. — While  some  of  the  folds  in  the  region  south 
of  Lake  Erie  are  limited  to  only  a  few  feet  in  vertical  extent,  it  is  sig- 
nificant that  they  do  not  commonly  show  close,  overturned,  and  recum- 
bent types,  which  are  very  common  in  minor  intra-formational  folds.  A 
close  fold  of  this  type,  occurring  in  the  Arbuckle  Mountains  of  Oklahoma, 
is  shown  in  Figure  10.  This  fold  is  in  the  weak  calcareous  beds  of  the 
Simpson  which  lie  between  the  heavy  Simpson  sandstones  and  the 
Arbuckle  limestone. 

To  the  east  of  the  Lake  Erie  region  at  Trenton  Falls,  New  York, 
intra-formational  folds  occur  in  the  Trenton  limestone  at  two  horizons, 
the  rest  of  the  strata  being  parallel  and  not  folded.  These  folds  recently 
have  been  illustrated  and  described  by  W.  J.  Miller.1  He  says: 

Within  the  folded  zones  the  layers  are,  in  rare  instances,  scarcely  dis- 
turbed; sometimes  they  are  only  gently  folded;  most  commonly  they  are 
highly  twisted  or  contorted;  while  occasionally  some  of  the  layers  are  broken, 
and  pushed  or  faulted  over  others. 

Earlier,  L.  Vanuxem  illustrated  and  described  these  folds  as  follows: 
For  thirty  or  more  feet  in  length,  and  from  three  to  five  feet  in  thickness, 
the  rock  exhibits  extraordinary  contortions  for  one  whose  layers  are  so  regu- 
larly disposed,  forming  almost  semicircular  curvatures,  and  not  unlike  the 
writhings  of  a  huge  serpent.  When  the  contortions  are  observed,  they  show  a 
crystallized  white  limestone,  enveloped  in  the  usual  calcareous  shaly  materials, 
proving  that  the  disturbance  was  caused  by  the  crystallization  of  the  white 
limestone  forming  a  layer.2 

Later,  the  same  folds  were  described  and  illustrated  by  T.  G.  White.3 
Folds  of  this  type  in  western  Pennsylvania  have  been  descrbed  by 
R.  R.  Hice  as  follows: 

At  the  site  of  Dam  No.  5  on  the  Ohio  River,  on  the  eastern  edge  of  the 
Beaver  quadrangle  between  the  towns  of  Rochester  and  Freedom,  a  recent 
railroad  cut  exposes,  in  a  distance  of  600  feet,  a  series  of  foldings  involving  the 
strata  between  the  base  of  the  Lower  Kittanning  clay  and  the  horizon  of 

'  W.  J.  Miller,  Jour.  Geol.,  XVI  (1908),  428-33. 

2  L.  Vanuxem,  Geol.  of  $d  Dist.  N.Y.  (1842),  p.  53. 

3  T.  G.  White,  Trans.  N.Y.  Acad.  Sci.  (1895),  pp.  71-96,  Plate  3 A. 


STUDIES  IN  MINOR  FOLDS  37 

the  Middle  (Upper)  Kittanning  coal  (about  35  feet)  in  no  way  involving  the 
underlying  strata  or  those  above  the  horizon  of  the  Middle  Kittanning.1 

W.  G.  McGee  has  described  some  similar  small  folds  and  faults  in  the 
Cedar  Valley  (Devonian)  limestone  of  northeastern  Iowa.2  While  the 
folds  are  within  the  single  formation  so  far  as  observed,  they  are  more 
gentle  than  intra-formational  folds  commonly  are,  and  in  the  illustration 
given,  the  deformation  is  near  the  surface.  The  folding  is  associated 
with  brecciation  in  the  limestone,  and  as  brecciation  was  coeval  with 
deposition,  the  deformation  and  brecciation  were  thought  to  have  been 
contemporaneous.  The  same  type  of  folds  occurs  in  the  Quaternary 
clays  along  the  Black  River  canal  feeder  about  3  miles  from  Boonville, 
New  York,  where  a  series  of  closely  folded  layers  in  a  folded  zone  occurs 
between  unfolded  parallel  strata  on  either  side.3  I.  C.  Russell  also 
describes  and  illustrates  intercalary  folds  in  Quaternary  deposits  in  the 
Lake  Mono  region  of  California,  and  concludes  that  they  were  formed 
in  some  manner  at  the  time  of  deposition.4  E.  M.  Kindle  explains 
folded  sands  and  clays  between  non-folded  beds  in  Nova  Scotia  and 
southern  Ontario  by  movement  of  soft  muds  beneath,  due  to  irregular 
weighting.5 

The  only  folds  of  this  type  found  in  the  Lake  Erie  region  are  extremely 
small  and  unimportant  (Fig.  22).  On  the  northeast  side  of  Twenty  Mile 
Gulf,  one-fourth  mile  west  of  the  Pennsylvania-New  York  state  line,  a 
small  fold  in  the  vertical  bank  is  inclosed  between  horizontal  strata 
above  and  below.  The  fold  is  up  about  25  feet  in  an  8o-foot  bank. 
Only  about  5  feet  of  strata  are  involved.  The  thickening  of  the  strata 
above  the  fold  either  side  of  the  crest  indicates  that  a  few  of  the  beds 
were  slightly  deformed  soon  after  their  deposition,  before  the  super- 
jacent  stratum  was  deposited,  as  the  latter  fills  in  the  depression  either 
side  of  the  crest  of  the  fold.  The  second  and  third  beds  above  the  fold 
become  uniform  in  thickness  and  horizontal  in  position. 

Parallel  folds. — Numerous  small  folds  with  axes  parallel  with  the 
trend  of  valleys  occur  in  the  floor  of  many  of  the  post-glacial  valleys 
of  the  area.  The  folds  generally  are  small,  involve  only  a  few  feet  of 
strata,  and  usually  are  limited  entirely  to  the  valley  floor,  affecting  the 

1  R.  R.  Hice,  Bull.  GeoL  Soc.  Amer.,  XXII  (1910),  716-17,  Abs. 

2  W.  G.  McGee,  Eleventh  Ann.  Kept.  U.S.G.S.,  Part  i  (1889-90),  pp.  337~38. 

3  L.  Vanuxem,  GeoL  jd  Dist.  N.Y.  (1842),  pp.  213-15.  • 

<I.  C.  Russell,  8th  Ann.  Kept.  U.S.G.S.,  Part  i  (1886-87),  PP-  307-10. 
s  E.  M.  Kindle,  Butt.  GeoL  Soc.  Amer.,  XXVIII  (1917),  323-34. 


38  STUDIES  IN  MINOR  FOLDS 

walls  of  the  valley  in  only  a  few  instances.  This  type  of  fold  occurs  in 
many  parts  of  the  area,  but  is  especially  common  in  the  steep,  post- 
glacial valleys  in  the  vicinity  of  Meadville,  and  in  the  southern  tribu- 
taries of  Walnut  Creek,  5  miles  southeast  of  Erie.  Figures  23  and  24 
represent  two  of  the  parallel  types  of  folds  from  the  Meadville  region. 
In  Figure  23  the  box  in  the  right  foreground  rests  on  the  crest  of  the 
anticline  over  the  joint  crack  along  the  axis.  The  stream  crosses  the 
crest  and  flows  diagonally  across  the  valley  down  the  dip  on  the  right 


FIG.  22. — Small  fold  with  strata  horizontal  above  and  below  it  in  Twenty  Mile 
Gulf  I  mile  west  of  New  York  state  line. 

limb.  At  the  left  the  beds  are  dipping  into  the  north  bank  of  the 
stream.  The  fold  is  in  sandy  beds  2  to  3  inches  in  thickness  in  the 
upper  part  of  the  Riceville  shale.  It  is  about  30  feet  wide  and  160  feet 
long,  and  is  the  upper  one  of  a  series  of  four  occurring  in  this  ravine. 
Figure  24  shows  the  crest  of  a  fold  beneath  the  roots  of  a  tree  in  the 
edge  of  the  flood  plain.  The  strata  are  sandy  shales  in  the  upper  part 
of  the  Riceville  formation.  The  axis  is  N.5o°E.,  and  the  dip  near  the 
crest  is  34°NW.  and  30°SE.,  but  the  limbs  flatten  out  rapidly.  The 
fold  is  about  60  feet  wide  and  260  feet  long,  and  8  to  10  feet  of  exposed 
strata  are  involved.  While  folds  of  this  type  are  more  common  in  the 
smaller  valleys  with  narrow  floors  and  steep  sides,  some  also  are  found 
in  the  creek  bottoms  of  the  larger  streams  tributary  to  Lake  Erie. 

Transverse  folds. — The  most  important  folds  of  the  area  are  those 
with  axes  transverse  to  the  valley,  so  they  are  exposed  in  the  flood 


STUDIES  IN  MINOR  FOLDS 


39 


plains,  terraces,  and  valley  walls.     The  width  of  the  folds  varies  from  a 
few  feet  to  over  500  feet.     The  rise  of  the  strata  from  the  side  to  the 


FIG.  23.  —  Anticline  having  axis  parallel  with  valley,  in  Bemistown  Run, 
northwest  of  Meadville,  Pa. 


miles 


FIG.  24. — Small  anticline  in  the  bottom  of  Park  Avenue  ravine,  at  the  north 
edge  of  Meadville,  Pa. 

center  of  the  fold  is  seldom  more  than  12  feet.  Numerous  terraces, 
varying  from  10  to  40  feet,  and  a  few  as  high  as  60  or  80  feet,  are  deformed 
by  the  folds.  While  the  axes  of  a  few  folds  trend  about  north  and  south, 


40  STUDIES  IN  MINOR  FOLDS 

and  a  few  others  east  and  west,  the  majority,  about  three-fifths,  trend 
in  a  northwesterly  direction,  and  the  remaining  ones  in  a  northeasterly 
direction. 


FIG.  25. — Unsymmetrical    anticline    in    1 8-foot    terrace    f    mile    southeast    of 
Girard,  Pa. 


FIG.  26. — Anticline  along  Twenty  Mile  Creek  \  mile  south  of  the  N.Y.,  C.  & 
St.  L.  R.R.,  5  miles  east  of  North  East,  Pa. 

In  this  area  the  strata  involved  are  the  Upper  Devonian  and  Lower 
Mississippian.     To  the  east,  in  central  New  York,  numerous  faults  and 


STUDIES  IN  MINOR  FOLDS  41 

folds  have  been  recognized  in  formations  extending  in  age  from  Cam- 
brian1 to  Devonian.2  To  the  northeast,  on  both  sides  of  Lake  Ontario, 
folds  occur  in  the  Queenston  shale  of  either  Silurian  or  Ordovician  age. 
Besides  the  transverse  folds  used  in  other  connections  in  Figures  8,  12, 
31,  33,  38,  and  41,  a  few  other  characteristic  ones  will  be  illustrated  and 
described.  One  of  the  more  open  folds,  quite  unsymmetrical  in  form, 
is  shown  in  Figure  25.  This  asymmetry  is  clearly  indicated  by  the 
difference  in  dip  in  the  two  limbs.  The  dip  to  the  right  toward  the 
northeast  is  17°,  while  to  the  left  of  the  crest  it  is  37°  to  the  southwest. 
The  fold  is  in  the  lower  part  of  the  Girard  shales,  which  here  contain 
numerous  sandstone  beds.  While  most  of  the  sandstone  beds  are  only 
i  or  2  inches  thick,  the  one  seen  most  clearly  in  the  picture  has  a  thick- 
ness of  7  inches.  The  strata  rise  14  feet  from  the  sides  to  the  center  of 
the  fold,  and  it  has  a  total  width  of  300  feet.  The  axis  trends  N.8o°W., 
and  about  one-fourth  mile  to  the  northwest  it  is  exposed  again  where  a 
western  tributary  of  Elk  Creek  crosses  it. 

Another  transverse  fold,  much  closer  than  that  shown  in  Figure  25, 
is  illustrated  in  Figure  26.  The  axis  of  this  fold  is  N.25°E.,  and  the 
dip  on  the  left  toward  the  northwest  is  26°,  while  on  the  right  toward 
the  southeast  it  is  40°.  The  closer  part  of  the  fold  is  only  30  feet  wide, 
but  the  total  width  is  about  300  feet.  A  very  abrupt  bend  occurs  in 
the  strata  of  the  southeast  limb,  where  the  highly  dipping  beds  meet 
those  of  more  gentle  dip.  This  abrupt  bend  has  almost  reached  the 
point  of  rupture.  This  fold  is  in  the  formation  called  Portage  by  the 
earlier  writers,3  but  later  studies4  seem  to  place  it  in  the  Chemung. 
The  rocks  consist  of  numerous  thin  sandstone  beds  separated  by  loose 
dark-gray  shales.  This  is  one  of  the  small  series  of  folds  in  which  the 
axes  have  a  northeast  trend.  It  also  is  one  in  which  the  1 4-foot  terrace 
is  markedly  deformed  for  a  long  distance  above  the  crest  of  the  fold. 

Another  fold  of  this  general  type,  which,  however,  is  transverse  not 
to  a  valley  but  to  the  direction  of  the  lake  shore,  is  shown  in  Figure  27. 
It  is  in  a  low  cliff  along  the  lake  shore  3  miles  east  of  Erie.  The  axis 
is  N.20°W.  It  is  distinctly  unsymmetrical  in  form,  having  a  northeast 
dip  of  45°  and  a  southwest  dip  of  14°.  The  closer  part  of  the  fold  is 
60  feet  wide.  Thin  flaggy  sandstones  of  the  Chemung  are  separated 

1  J.  B.  Woodworth,  N.Y.  State  Mns.  Bull.  107  (1907),  p.  21. 

2  P.  F.  Schneider,  Amer.  Jour.  Sci.,  4th  Ser.,  XX  (1905),  316,  311. 

3 1.  C.  White,  Second  Geol.  Surv.  Pa.,  Kept.  Q<  (1881),  pp.  119-20;  and  J.  Hall, 
Nat.  Hist.  N.Y.  4th  Dist.,  Part  4  (1843),  P-  238. 

4  J.  M.  Clarke,  N.Y.  State  Mus.  Butt.  69  (1902),  p.  853. 


42  STUDIES  IN  MINOR  FOLDS 

by  thin  layers  of  shale.     The  loose  top  of  the  fold  is  thrust  up  into  the 
glacial  till. 

One  of  the  very  small  transverse  folds  is  shown  in  Figure  28.     It 
has  a  width  of  about  50  feet,  and  is  of  the  gentle,  open  type.     It  occurs 


FIG.  27. — Anticlinal  fold  with  uneroded  crest,  3  miles  east  of  Erie,  Pa. 


FIG.  28. — Small  anticline  along  Elk  Creek  f  mile  west  of  Miles  Grove,  Pa. 

in  the  flaggy  sandstones  called  Portage,  in  the  east  bank  of  Elk  Creek, 
about  three-fourths  of  a  mile  west  of  Miles  Grove,  Pennsylvania. "  Thin 
sandstone  beds  and  sandy  shales  are  interbedded  with  the  thicker  beds 
of  sandstone.  This  small  fold  with  its  axis  N.30°W.  seems  but  a  small 


STUDIES  IN  MINOR  FOLDS  43 

buckle  on  a  much  larger  anticline  to  the  southeast.  The  axis  of  the 
latter  trends  N.55°E.,  so  the  axes  of  the  smaller  and  larger  folds  are 
about  at  right  angles.  Out  in  the  channel  to  the  left  of  the  picture,  the 
heavy  sandstone  has  been  completely  cut  away  at  the  crest,  and  is  seen  to 
be  breaking  beneath  and  at  the  left  of  the  knapsack.  This  fold  illustrates 
the  way  in  which  the  loose  shales  are  readily  eroded  from  the  crest  by 
the  stream,  while  a  heavy  sandstone  bed  may  resist  the  erosive  work 
of  the  stream  for  a  considerable  period  of  time. 

Faults. — Under  the  heading  of  local  structures  it  has  been  noted 
that  the  rocks  of  this  area,  besides  the  folds,  are  affected  also  by  thrust 
faults.  These  faults  have  only  a  small  amount  of  displacement,  Vary- 
ing from  a  few  inches  to  7  feet.  In  the  majority  of  cases  the  fault 
planes  are  low,  and  the  horizontal  displacement  greatly  exceeds  the 
vertical.  In  many  instances  the  faults  are  in  some  way  connected  with 
folds,  but  this  is  not  always  the  case  with  some  of  the  smaller  ones. 

Faults  unrelated  to  folds. — Illustrations  of  two  small  thrust  faults,  in 
which  no  relation  to  folds  was  discovered,  are  shown  in  Figures  29  and 
30.  In  Figure  29  the  fault  is  in  the  lower  part  of  a  30-foot  bank  of 
Girard  shales  on  the  east  side  of  Little  Elk  Creek,  3!  miles  southeast  of 
Girard,  Pennsylvania.  The  fault  plane  here  dips  northeast  about  20°. 
To  the  right  of  the  picture  it  dips  more  steeply^  as  it  goes  beneath  the 
floor  of  the  valley.  The  amount  of  displacement  is  thought  to  be  slight, 
as  it  is  all  taken  up  in  the  loose  shales  at  the  left.  A  brecciated  zone 
occurs  back  of  the  hammer. 

The  second  illustration  of  a  small  fault  unrelated  to  a  fold  is  shown 
in  Figure  30.  In  this  fault  the  plane  dips  35°  to  the  southeast.  It 
shows  only  about  8  feet  above  the  level  of  Sixteen  Mile  Creek,  along 
which  it  occurs  3  miles  southeast  of  North  East,  Pennsylvania.  It 
seems  to  have  less  than  a  foot  of  displacement.  Above  the  fault  plane 
the  movement  has  been  taken  up  by  the  loose  shales,  there  being  about 
100  feet  of  them  above  in  the  bank. 

Faults  related  to  folds.— Many  of  the  thrust  faults  of  the  area  are 
definitely  related  to  folds,  or  are  closely  associated  with  them  under 
conditions  suggestive  of  some  relation.  In  connection  with  the  descrip- 
tion of  the  fold  in  Figure  4,  it  was  noted  that  the  marked  asymmetrical 
anticline  was  broken  at  the  crest,  and  that  the  strata  above  it  were 
broken  and  faulted.1  Figures  31  and  32  show  faults  below  grading  into 
folds  above.  In  Figure  3 1  the  fault  is  in  the  middle  of  the  broad,  gentle 

JT.  C.  Chamberlin  and  R.  D.  Salisbury,  Geology,  I  (1909),  516,  Fig.  421;  and 
Bailey  Willis,  Thirteenth  Ann.  Kept.  U.S.G.S.,  Part  2  (1891-92),  Plate  95. 


44 


STUDIES  IN  MINOR  FOLDS 


anticline.  The  fold  is  symmetrical,  with  a  dip  of  8°  in  each  limb.  The 
direction  of  the  axis  is  N.6o°W.  The  fold  is  140  feet  wide  and  has  a 
rise  of  4  feet  at  the  center.  The  plane  of  the  small  fault  in  the  center, 


FlG.  29.— Thrust  fault  in  east  bank  of  Little  Elk  Creek,  3^  miles  southeast  of 
Girard,  Pa. 


FIG.  30. — Small  thrust  fault  in  high  bank  of  shale  along  Sixteen  Mile  Creek, 
3  miles  southeast  of  North  East,  Pa. 

dipping  northeast  20°,  extends  below  the  valley  floor.  The  displace- 
ment in  the  fault  is  slight,  the  throw  and  heave  being  nearly  equal — the 
former  10  inches  and  the  latter  9  inches.  This  fold  and  fault  are  in  a 


STUDIES  IN  MINOR  FOLDS 


45 


terrace  at  the  south  edge  of  the  bridge  crossing  Elk  Creek  just  west  of 
Girard.     The  terrace  is  32  feet  high  at  the  bridge  and  increases  to  about 


FIG.  31. — Small  thrust  fault  in  center  of  a  symmetrical  anticline,  Elk  Creek,  at 
west  edge  of  Girard,  Pa. 


FIG.  32. — Thrust  fault  below  grading  into  a  fold  above,  Walnut  Creek,  i  mile  west 
of  Swanville,  Pa. 

38  feet  over  the  crest  of  the  fold.  In  Figure  32  the  plane  of  the  thrust 
fault  emerges  from  beneath  the  water  and  the  fault  below  grades  into 
an  unsymmetrical  fold  above.1  In  accordance  with  this  condition  are 

1 T.  C.  Chamberlin  and  R.  D.  Salisbury,  Geology,  I  (1909),  516,  Fig.  422. 


46 


STUDIES  IN  MINOR  FOLDS 


the  experiments  of  Bailey  Willis  in  producing  folds  and  faults  by  lateral 
pressure.1     This  fault  is  in  a  20-foot  terrace  on  the  west  side  of  Walnut 


FIG.  33. — Unsymmetrical  fold  with  two  thrust  faults,  the  larger  one  in  the 
upper  sandstone  bed  and  the  smaller  in  the  lower  bed  at  the  left  edge  of  the  picture, 
Paine  Creek,  6  miles  east  of  Painesville,  Ohio. 


FIG.  34. — Two  thrust  faults  with  a  small  anticline  between,  the  larger  fault 
being  at  the  left  of  the  fold,  along  a  southern  tributary  of  Elk  Creek,  f  mile  south  of 
Girard,  Pa. 

Creek  between  the  two  railroads  10  miles  southwest  of  Erie.     The  fault 
plane  dips  30°  south,  and  the  throw  is  about  2  feet  6  inches. 

1  Bailey  Willis,  Thirteenth  Ann.  Kept.  U.S.G.S.,  Part  2  (1891-92),  Plates  91,  93. 


STUDIES  IN  MINOR  FOLDS  47 

Other  ways  in  which  faults  are  related  to  folds  are  shown  in  Figures  33 
and  34.  The  illustration  in  Figure  33  shows  a  marked  unsymmetrical 
fold  and  two  faults.  The  fold  is  47  feet  wide,  with  a  southwest  dip  of 
8°  and  a  northeast  dip  of  52°.  The  axis  is  N.6o°W.  The  upper  n-inch 
sandy  stratum  has  been  faulted  at  the  right  of  the  fold,  being  thrust 
4  feet  6  inches  over  the  horizontal  part  of  the  same  stratum  at  the 
right.  At  an  interval  of  3  feet "  8  inches  below  this  stratum  is  a  second 
1 6-inch  sandstone  bed,  which  because  of  the  fold,  is  carried  beneath  the 
level  of  the  creek  at  the  right.  This  lower  heavy  stratum,  which  is 
sharply  folded  toward  the  right,  is  over  thrust  at  the  left  edge  of  the 
picture,  for  a  distance  of  21  inches,  where  the  fault  plane  dips  17°  toward 
the  northeast.  The  high  part  of  the  bank  above  the  fold  is  about  40  feet. 
This  fold  and  the  faults  are  just  east  of  the  wagon  bridge  across  Paine 
Creek,  six  miles  east  of  Painesville,  Ohio,  and  are  in  the  Chagrin  formation. 

Still  another  relation  of  faults  to  folds  is  shown  in  Figure  34,  where 
two  faults  occur  on  either  side  of  a  small  anticline.  This  small  fold  is 
well  down  on  the  west  limb  of  a  much  larger  anticline  which  seems  to 
be  the  northwestward  continuation  of  the  one  shown  in  Figure  25. 
The  anticline  in  Figure  34  is  in  a  low  terrace  consisting  of  5  feet  of  shales 
and  sandstones,  two  of  the  beds  of  sandstone  being  respectively  4  and 
8  inches  thick.  In  the  fault  at  the  left  of  the  anticline  the  throw  is 
2  feet  3  inches  and  the  heave  4  feet  6  inches,  and  the  fault  plane  dips 
30°  southwest.  In  the  smaller  fault  at  the  right  of  the  anticline 
the  throw  is  5  inches  and  the  heave  8  inches.  These  folds  and  faults 
occur  along  a  southwestern  tributary  of  Elk  Creek,  one-fourth  mile 
northwest  of  the  exposure  of  the  fold  shown  in  Figure  38.  Here  the 
overthrusts  are  on  the  west  limb  and  toward  the  center  of  the  large 
anticline.  In  the  exposure  of  the  same  large  fold  downstream  about 
1,200  feet,  there  is  one  larger  fault  with  a  throw  of  6  feet  and  6  inches, 
the  trace  of  the  fault  plane  being  N.8o°W. 

In  some  instances  thrust  faults,  while  not  directly  associated  with 
folds,  occur  only  a  short  distance  from  them,  and  so  are  thought  to 
have  resulted  from  the  same  stresses  that  formed  the  folds.  This  rela- 
tion of  fault  and  fold  exists  in  the  Twenty  Mile  Gulf  one-fourth  mile 
south  of  the  New  York,  Chicago  and  St.  Louis  Railway.  A  marked 
unsymmetrical  anticline  with  steeper  dip  to  the  southeast  occurs  in  the 
terrace  on  both  sides  of  the  creek.  About  100  feet  upstream  there  is  a 
thrust  fault  with  the  trace  of  a  plane  parallel  with  the  axis  of  the  fold, 
N.25°E.,  and  both  are  parallel  with  a  bank  100  feet  high  a  short  distance 
to  the  southeast.  The  fold  is  shown  in  Figure  26. 


48  STUDIES  IN  MINOR  FOLDS 

CONSIDERATION   OF   THE    ORIGIN   OF   FOLDS   AND   FAULTS 

Many  and  varied  causes  have  been  assigned  for  the  origin  of  folds. 
A  large  number  have  been  formed  in  regions  of  igneous  activity,  by  the 
intrusion  of  large  magmatic  masses  beneath  and  into  sedimentary  rocks. 
Other  causes  assigned  are:  heat  of  igneous  rocks,  rise  in  temperature 
since  the  glacial  period,  pressure  of  natural  gas,  glacial  pressure,  drag 
of  glaciers,  flexing  by  ice  pressure,  drag  of  icebergs,  landslides,  pressure 
developed  by  alteration  of  iron  sulphides,  weathering,  compacting  of 
soft  sediments,  solution,  crystallization,  differential  movements  in  large 
faults,  pressure  of  valley  walls,  relief  from  pressure,  pressure  of  sedi- 
ments in  a  delta,  and  tangential  compression. 

Igneous  activity. — In  the  area  under  consideration  the  folds  are 
thought  to  have  had  no  relation  to  igneous  activity,  as  the  nearest 
igneous  rocks  known  are  some  dikes  at  Syracuse,  Dewitt,  Manheim, 
and  Ithaca,  New  York,1  150  miles  to  the  east.  However,  in  other  parts 
of  the  country,  many  folds  have  resulted  from  the  intrusion  of  igneous 
material  from  beneath  into  the  sedimentary  rocks.  Numerous  examples 
of  folds  resulting  from  these  intrusions  are  found  in  the  Cascade,  Sierra 
Nevada,  and  Rocky  mountains,  and  many  folios  of  the  United  States 
Geological  Survey2  show  structure  sections  in  which  the  folds  are  due  to 
igneous  activity.  While  folding  from  this  cause  generally  results  from 
stresses  initiated  by  the  injection  of  large  masses  of  igneous  material  up 
through  the  sedimentary  beds,  a  more  indirect  cause  suggested  in 
a  formation  adjacent  to  such  material  is  the  expansion  of  that  for- 
mation by  heat  transmitted  from  igneous  rocks  above  it.  A.  W.  G. 
Wilson  has  described  some  folds  in  the  Keweenawan  dolomite  at  Cook 
Point  in  the  Nipigon  Basin  of  Canada,  which  are  covered  by  a  sheet  of 
diabase  120  feet  thick,  the  anticlinal  arches  projecting  up  into  the 
diabase.  Concerning  the  origin  of  the  folds  he  says: 

No  dikes  were  found  in  the  dolomite,  though  they  may  occur.  The  folds 
may  have  been  caused  by  their  intrusion,  or  as  seems  more  probable  in  the 
absence  of  any  evidence  that  dikes  are  presentj  they  may  have  resulted  from 
the  expansion  of  the  dolomite  when  heated  by  the  molten  trap.3 

Inasmuch  as  no  igneous  rocks  occur  in  or  near  the  lake  region  studied, 
folds  cannot  be  attributed  to  heat  from  them. 

1  P.  F.  Schneider,  Amer.  Jour.  Sci.,  4th  Ser.,  Ill  (1897),  458. 

2  Structure  Section  Sheets,  U.S.G.S.  Folios:  Phillipsburg,  Mont.,  No.  196;  Livings- 
ton, Mont.,  No.  i;   Little  Belt,  Mont.,  No.  56;   Bradshaw  Mts.,  Ariz.,  No.  176;  Santa 
Cruz,  Cat.,  No.  163;  Downievitte,  Col.,  No.  37;  Redding,  Cat.,  No.  136;  Truckee,  Cal., 
No.  39;  Mount.  Stuart,  Wash.,  No.  106;  Snoqualmie,  Wash.,  No.  139. 

3  A.  W.  G.  Wilson,  Geol.  Surv.  Canada  Mem.  i  (1910),  pp.  118,  119. 


STUDIES  IN  MINOR  FOLDS  49 

Rise  in  temperature  at  close  of  glacial  period. — This  cause  was  sug- 
gested by  G.  K.  Gilbert  for  some  of  the  small  folds  in  the  eastern  part 
of  the  area  in  western  New  York.  He  discovered  several  small  post- 
glacial anticlines  in  the  horizontal  limestones  of  Jefferson  County,  New 
York,  and  in  the  shales  near  Dunkirk,  in  the  western  part  of  the  state, 
and  suggests  that  they  may  have  resulted  from  expansion  caused  by 
the  warming  up  of  the  surface  layers  of  the  rocks  as  they  recovered  from 
the  cold  of  the  glacial  period.1  In  a  paper  on  "Some  New  Geologic 
Wrinkles"  (given  before  the  American  Association  for  the  Advance- 
ment of  Science  at  Buffalo),  he  says: 

In  Jefferson  and  Chautauqua  Counties,  New  York,  there  have  been 
observed  small  anticlinal  ridges  involving  strata  otherwise  little  disturbed. 
Their  relation  to  glacial  deposits  and  striation  show  them  to  be  of  post-glacial 
origin,  and  they  are  believed  to  have  arisen  from  the  horizontal  expansion  of 
superficial  strata  consequent  on  post-glacial  amelioration  of  climate.2 

While  water  from  the  glaciers  may  have  cooled  the  rocks  below  their 
normal  temperature,  it  is  thought  that  the  rise  resulting  from  the  reces- 
sion of  the  ice  necessary  to  bring  them  back  to  their  normal  tempera- 
ture again,  would  not  be  sufficient  to  set  up  lateral  stresses  in  them. 
Then,  too,  a  type  of  folds  and  faults  is  common  in  this  region  which  is 
not  found  in  other  glaciated  areas  where  there  was  a  corresponding  rise 
in  temperature  after  the  ice  receded. 

Pressure  due  to  expansion  of  ice. — In  describing  and  illustrating 
some  of  the  folds  of  western  New  York,  in  the  eastern  part  of  this  area, 
James  Hall  suggested  the  uplifting  by  ice  as  a  cause  for  some  of  them. 
He  notes  several  along  the  shore  of  Lake  Erie,  and  says : 

In  other  parts  of  the  district  these  uplifts  have  produced  lines,  which, 
being  more  easily  excavated,  have  become  the  channels  of  streams.  Many 
beds  of  streams  present  this  appearance, but  in  most  cases  I  have  been  inclined  to 
refer  the  apparent  phenomena  to  the  very  partial  uplifting  of  the  strata  by  ice. 

Very  many  instances  doubtless  are  due  to  this  latter  cause,  but  there 
are  others  which  cannot  be  referred  to  such  an  influence.  He  then 
gives  an  illustration  of  a  fold  in  the  south  branch  of  the  Cattaraugus 
Creek,  in  which  the  strata  beneath  the  bed  and  in  both  walls  are  involved. 
He  says  of  the  origin  of  this  fold: 

The  disturbance  here  is  so  great,  that  it  seems  due  to  some  more  powerful 
agency  than  the  freezing  of  the  water.  Still,  however,  so  many  points  present 

1  G.  K.  Gilbert,  Amer.  Jour.  Sci.,  3d  Ser.,  XXXII  (1886),  324;  and  Amer.  Assoc. 
Adv.  Sci.  Proc.,  XXXV  (1886),  227. 

2  G.  K.  Gilbert,  Proc.  Amer.  Assoc.  Adv.  Sci.,  XXXV   (1886),  227. 


50  STUDIES  IN  MINOR  FOLDS 

similar  appearances,  which  are  evidently  due  to  the  latter  cause,  that  it  is  not 
easy  to  decide.1 

Smallwood  and  Hopkins  have  suggested  that  the  presence  of  run- 
ning water  in  most  of  the  valleys  would  prevent  the  rocks  beneath  from 
freezing.2  However,  the  shifting  of  the  stream  laterally  across  the 
valley  floor  would  expose  rocks  beneath  low  flood  plains  to  frost  action 
in  the  course  of  this  lateral  shifting.  It  is  thought  that  the  pressure 
resulting  from  ice  expansion  has  not  been  an  important  initial  cause  of 
deformation  of  the  area.  After  the  rocks  have  been  deformed,  and  the 
edges  of  the  strata  exposed  by  erosion,  the  expansion  of  ice  between 
beds  doubtless  does  increase  the  deformation  by  lifting  parts  of  the 
strata  higher,  thus  materially  increasing  their  dip.  In  the  central  part 
of  some  of  the  folds,  numerous  joint  cracks  occur,  the  strata  are  loose, 
and  high  dips  are  common.  Part  of  the  work  of  loosening  and  raising 
these  beds  doubtless  is  due  to  the  expansion  of  ice  between  the  strata. 
Note  that  these  conditions  are  shown  well  at  the  crest  of  the  fold  illus- 
trated in  Figure  24. 

Alteration  of  iron  sulphides. — A  series  of  small  folds  near  Cleveland 
has  been  described  by  F.  R.  Van  Horn.3  He  has  computed  that  in  the 
alteration  of  iron  sulphides  to  iron  sulphates  and  alum-like  compounds 
there  would  be  nearly  a  threefold  increase  in  volume.  He  thinks  that 
locally  there  has  been  sufficient  iron  sulphide  in  the  rocks  so  that  the 
marked  increase  in  volume  due  to  the  alteration  would  cause  pressure 
capable  of  forming  the  folds. 

At  various  localities  in  the  area  considerable  aluminous  material  in 
the  form  of  incrustations  on  the  shales  is  found.  Notable  deposits 
occur  on  the  shales  involved  in  the  fold  and  fault  shown  in  Figure  31. 
However,  numerous  deposits  of  this  same  type  have  been  observed  on 
the  shales  at  various  places  where  no  folds  have  been  developed,  and 
furthermore,  most  of  the  folds  of  the  area  under  consideration  have  no 
such  deposits  of  aluminous  material  related  to  them. 

Another  point  to  be  considered  is  the  solubility  of  the  iron  sulphate. 
In  a  moist  room,  where  water  is  not  present  in  a  form  to  carry  away 
the  products  of  alteration,  an  incrustation  of  tiny  crystals  will  form  in 
a  few  months  on  the  surface  of  marcasite  of  a  porous,  impure  variety. 
Were  the  alteration  to  take  place  in  the  shale  below  the  surface  of  the 

1  James  Hall,  Geol.  4th  Dist.  N.Y.,  Part  4  (1843),  PP-  293~97- 

2  W.  M.  Smallwood  and  T.  C.  Hopkins,  Bull.  Syracuse  Univ.,  4th  Ser.,  No.  i 
( 1903),  pp.  18-24. 

F.  R.  Van  Horn,  Bull.  Geol.  Soc.  Amer.,  XXI  (1909),  771-73. 


STUDIES  IN  MINOR  FOLDS  51 

ground,  a  minor  part  might  be  precipitated,  but  the  major  part  would 
be  taken  into  solution  and  carried  away.  If  then  iron  sulphate,  because 
of  ready  solubility,  is  largely  carried  away  by  ground- water,  is  it  possible 
that  the  process  of  alteration  of  iron  sulphide  still  may  be  an  important 
factor  in  producing  stresses  capable  of  deforming  rocks  ?  Is  there  a 
marked  increase  in  volume  in  the  alteration  of  the  iron  sulphides  to  the 
hydroxides?  C.  R*  Van  Hise  speaks  of  the  alteration  of  the  iron  sul- 
phides as  follows: 

The  minerals  pyrite  and  marcasite  may  by  oxidation  pass  directly  into 
(i)  hydrated  sesquioxide  of  iron,  of  which,  ordinarily,  limonite  (not  crystal- 
lized; sp.  gr.  3.80)  is  the  most  common  kind;  (2)  magnetite  (isometric;  sp. 
gr.  5 . 174) ;  (3)  ferrous  sulphate  which  may  be  removed  in  solution;  or  (4)  may 
be  decomposed  by  further  oxidation,  either  at  the  place  of  formation  or  else- 
where after  a  longer  or  shorter  time,  into  hydrated  sesquioxide  of  iron,  ordi- 
narily limonite.1 

In  regard  to  volumetric  changes  in  this  alteration  he  says: 

In  the  change  of  pyrite  to  limonite,  the  volume  is  increased  2 .93  per  cent; 
to  magnetite,  is  decreased  37.48  per  cent;  in  the  change  from  marcasite  to 
limonite  the  volume  is  decreased  o.  14  per  cent.2 

Thus  it  is  seen  by  the  alteration  of  the  pyrite  to  limonite  the  volume 
is  increased  less  than  3  per  cent,  and  by  the  alteration  of  marcasite  to 
limonite  there  is  a  real  though  slight  decrease  in  volume.  So  it  is  the 
form  in  which  iron  sulphide  occurs  that  determines  whether  there  be  an 
increase  or  decrease  in  volume  when  alteration  takes  place.  Even 
when  the  alteration  of  pyrite  takes  place,  it  is  believed  that  the  slight 
increase  in  volume  would  not  be  effective  in  producing  stresses  capable 
of  folding  the  rocks.  This  idea  is  borne  out  by  the  fact  that  a  forma- 
tion like  the  Huron  shale,  which  contains  much  more  pyrite  than  the 
Chagrin  formation,  has  not  been  deformed  by  the  weathering  of  pyrite. 

Still  another  factor  to  be  considered  is  the  form  of  the  deformation. 
It  is  noteworthy  that  while  small  anticlines  are  described  by  Van  Horn, 
there  is  also  a  monocline,  indicating  that  in  one  instance  the  stress 
resulted  in  a  different  type  of  fold.  The  folds  are  post-glacial,  as  their 
sharp  crests  protrude  into  the  glacial  deposits  above.  The  very  fact 
that  sharp  anticlines  have  been  formed  indicates  that  the  horizontal 
component  in  the  stresses  has  been  relatively  large.  Unless  concen- 
trations of  iron  sulphide  were  in  linear  form,  deformation  due  to  increase 
in  volume,  with  vertical  stresses  predominating,  would  form  domelike 

1  C.  R.  Van  Hise,  U.S.  Geol.  Surv.  Mono.  47  (1904),  pp.  214,  215. 

2  C.  R.  Van  Hise,  ibid. 


52  STUDIES  IN  MINOR  FOLDS 

uplifts  instead  of  anticlines.  Furthermore,  the  disturbance  goes  deep 
enough  to  involve  parts  of  the  unweathered  shale,  thus  indicating  that 
the  alteration  of  the  materials  in  the  shale  is  not  an  important  factor  in 
their  deformation. 

While  an  important  suggestion  has  been  given  in  calling  specific 
attention  to  this  phase  of  alteration  of  iron  sulphides,  it  does  not  seem 
probable  that  this  alteration  in  the  shales  has  been  an  important  factor 
in  their  deformation,  because  numerous  folds  occur  where  the  content 
of  the  iron  sulphide  is  very  low,  and  at  other  places,  where  much  is 
present,  and  the  alteration  products  abundant  on  the  surface,  no  defor- 
mation has  occurred.  The  process  is  thought  to  be  unimportant,  too, 
because  of  the  solubility  of  iron  sulphate,  because  the  anticlines  seem  to 
indicate  lateral  stresses  rather  than  vertical,  and  because  unweathered 
parts  of  the  shale  are  involved  in  the  folds. 

Weathering  of  rocks. — For  a  large  number  of  very  small  folds,  weather- 
ing has  been  assigned  as  the  cause.  Generally  they  are  tiny  arches  a 
few  feet  across  and  involving  only  2  or  3  feet  of  strata.  Such  tiny  arches 
are  of  frequent  occurrence  in  the  walls  and  floors  of  valleys,  and  in  the 
sides  and  bottoms  of  quarries.  In  some  instances  a  single  bed  is  arched 
up,  as  in  the  case  of  the  Niagara  limestone  in  the  bottom  of  the  Lyons 
quarry  along  the  Des  Plaines  River,  at  the  southwestern  edge  of  Chicago. 

Several  thin  beds  may  be  involved,  as  in  the  case  of  a  fold  illustrated 
and  described  by  M.  R.  Campbell,  found  in  the  central  part  of  Logan 
County,  Arkansas,  50  miles  east  of  Fort  Smith.1  About  two  feet  of 
strata  show  distinct  arching,  but  being  sandstones  the  strata  are  much 
broken,  while  the  rocks  seem  to  be  affected  laterally  for  only  3  or  4  feet. 
He  considers  creep  and  freezing  as  possible  causes,  but  thinks  expansion 
due  to  weathering  the  most  probable  one.  He  speaks  of  the  complexity 
of  the  process,  noting  that  it  involves  both  chemical  and  mechanical 
changes  of  a  nature  to  increase  the  volume.  However,  he  decides  that 
the  most  important  element  is  the  opening  of  joints  and  cleavage  fissures, 
and  also  notes  the  possible  effect  of  ice  and  roots  in  the  cracks,  but  says : 

Although  the* amount  of  opening  in  each  joint  is  small,  the  aggregate  of 
hundreds  of  thousands  of  joints  would  tend  to  set  up  stresses  parallel  to  the 
bedding,  and  in  course  of  time  these  stresses  would  reach  the  point  of  rupture 
of  the  beds  involved,  and  a  fault  or  fold  would  be  produced.2 

In  general,  joint  cracks  are  evidence  of  lengthening  of  a  stratum  or 
a  contraction  of  the  material  in  it.  If  numerous  joint  cracks  are  open, 

1  M.  R.  Campbell,  Jour.  Geol.,  XIV  (1906),  718-21. 

2  M.  R.  Campbell,  ibid. 


STUDIES  IN  MINOR  FOLDS  53 

lateral  stresses  should  be  relieved  by  closing  the  cracks  rather  than  by 
arching  the  strata.  In  a  region  in  which  folds  are  common,  the  numer- 
ous open  joints  in  one  formation,  a  shale  of  the  Portage  group,  is 
assigned  by  the  present  writer  as  a  reason  why  almost  no  folds  were 
found  in  it.  Of  the  various  processes  of  weathering,  those  most  effec- 
tive in  producing  stresses  are  expansion,  due  to  rise  in  temperature  and 
to  freezing,  and  increase  in  volume  by  hydration. 

In  the  arching  of  a  single  stratum  it  is  believed  that  solar  heat 
chiefly  is  responsible,  just  as  sidewalks  are  buckled  and  steel  rails  bent 
by  the  excessive  heat.  Alteration  and  hydration  of  some  minerals 
cause  them  to  expand,  so  it  is  thought  that  stresses  competent  to  make 
the  tiny  folds  might  readily  result.  It  is  possible  that  some  of  the  tiny 
bucklings  in  ravines  in  this  area  may  be  due  to  these  weathering  processes. 

Stresses  due  to  crystallization  of  limestone. — The  force  of  crystalliza- 
tion of  limestone  is  given  by  L.  Vanuxem1  as  the  cause  of  the  intra- 
formational  folds  at  Trenton  Falls,  New  York.  Speaking  of  the  folds 
he  says: 

When  the  contortions  are  examined,  they  show  a  crystallized  white  lime- 
stone, enveloped  in  the  usual  calcareous  shaly  materials,  proving  that  the  dis- 
turbance was  caused  by  the  crystallization  of  the  white  limestone  forming  a 
layer;  which,  for  want  of  room  to  expand,  this  effect  being  simultaneous  with 
the  action  as  in  freezing  of  water,  was  forced  to  recoil,  and  thus  form  the 
contortions  noticed.  It  is  not  unlikely  that  the  water  of  the  mud  from  whence 
the  shale  was  produced,  was  the  solvent  of  the  calcareous  particles,  enabling 
them  to  assume  the  crystalline  state.  At  one  of  the  extremities  of  the  con- 
torted rock,  where  it  joins  the  undisturbed  portion,  it  is  broken  into  fragments, 
some  of  which  are  turned  on  end  by  the  violence  of  the  action. 

Without  doubt  there  is  a  power  in  crystallization  which  originates 
stresses  in  the  rocks.  A  familiar  example  of  this  force  is  seen  in  the 
ability  of  ground  ice  not  only  to  overcome  the  force  of  gravity  in  its 
growth,  but  also  to  raise  a  considerable  amount  of  soil,  stones,  and 
vegetable  matter  with  it.  Though  differing  quantitatively,  this  force 
of  crystallization  is  well  illustrated  in  the  formation  of  crystals,  often  of 
large  size,  of  such  minerals  as  staurolite  and  garnet.  Though  formed 
under  great  pressure,  these  minerals  in  their  growth  have  the  power  to 
force  the  materials  about  them  away  to  make  room  for  their  enlargement. 

But  though  the  force  of  crystallization  be  recognized  as  capable  of 
setting  up  some  local  stresses  in  the  rocks,  there  is  a  question  of  its 
application  to  the  phenomenon  of  folding.  W.  J.  Miller,  after  a  careful 

1  L.  Vanuxem,  Geol.  of  3d  Dist.  N.Y.  (1842),  p.  53. 


54  STUDIES  IN  MINOR  FOLDS 

examination  and  comparison  of  the  rocks  at  Trenton  Falls  in  the  folded 
zone  with  those  on  both  sides  of  it,  says:  "No  difference  in  crystalliza- 
tion can  be  detected."1  There  seems  no  reason  for  the  development  of 
marked  lateral  stresses  in  the  bed  of  limestone,  when  there  is  ample 
opportunity  for  vertical  expansion  in  the  shales  above  and  below  it. 
Furthermore,  no  instance  is  known  in  which  the  crystallization  of  any 
rocks  seems  to  have  developed  stresses  competent  to  deform  them, 
unless  it  be  those  around  the  salt  and  gypsum  domes  of  the  Gulf  Coastal 
Plain,  and  even  here  it  may  have  been  of  far  less  importance  than  the 
increase  in  volume  resulting  from  the  change  of  limestone  to  gypsum.2 

Deformation  by  solution  beneath. — There  are  two  types  of  conditions 
under  which  deformation  has  been  attributed  to  solution — the  forma- 
tion of  sinks  and  channels  by  the  solution  of  limestone,  and  the  solution 
of  an  underlying  stratum  of  salt  or  gypsum.  The  first  type  is  illustrated 
in  Miller  County,  Missouri,  southeast  of  the  center  of  the  state,  where 
two  Cambro-Ordovician  limestones,  the  Gasconade  and  the  St.  Elizabeth, 
have  been  affected.  In  this  area  it  is  said  of  the  St.  Elizabeth  formation : 

This  formation  is  complexly  flexured  very  much  the  same  as  the  Gas- 
conade underneath.  Steeply  dipping  beds  are  more  common  in  this  forma- 
tion than  in  any  other.  Many  of  them  have  resulted  from  the  falling  in  of 
the  roofs  of  caverns  due  to  underground  solution.3 

A  very  large  number  of  minor  dislocations  in  western  Kentucky  doubtless 
are  also  due  to  the  sinking  of  extensive  caverns.4 

Deformation  from  the  same  cause  has  taken  place  in  the  south- 
western lead  and  zinc  area,  where  enlargement  of  old  solution  cavities  in 
comparatively  recent  time  has  let  the  superjacent  Cherokee  shales  down 
and  deformed  them.5  There  also  is  a  more  indirect  way  in  which  solu- 
tion has  been  related  to  the  deformation  of  the  Cherokee  shales.  After 
the  latter  formation  was  deposited  in  the  solution  depressions  in  the  lime- 
stone, the  area  was  subjected  to  compression  in  post-Carboniferous 
times,6  and  the  shales,  being  less  competent  than  the  limestones,  have 
been  buckled  up  by  this  compression.7  In -these  instances  of  deforma- 

1 W.  J.  Miller,  Jour.  Geol.,  XVI  (1908),  430. 

2  W.  Kennedy,  Bull.  S.W.  Assoc.  Petroleum  Geologists,  I  (1917),  58,  59. 

3  S.  H.  Ball  and  A.  F.  Smith,  Geol.  Miller  Co.,  Mo.,  Bur.  Geol.  and  Min.  foa), 
I  (1903),  P-  58- 

«N.  S.  Shaler,  Geol.  Sun.  Ky.,  New  Ser.,  Ill  (1877),  231  (bottom  paging). 

5  Observation  of  writer  at  Commerce,  near  Miami,  Okla. 

6  C.  E.  Siebenthal,  Econ.  Geol.,  I  (1906),  128. 
?  Joplin  Folio,  No.  128  (1907),  p.  9. 


STUDIES  IN  MINOR  FOLDS  .  55 

tion  of  limestones  and  shales  as  a  result  of  solution,  several  areas  were 
affected,  each  entirely  unrelated  to  the  others  unless  two  solution 
cavities  were  near  together,  and  even  then  general  tangential  stresses 
did  not  result.  Small  folds  and  faults  possibly  may  be  a  minor  part  of 
major  movements  down  into  solution  cavities. 

The  second  type  of  conditions  under  which  deformation  has  been 
attributed  to  solution — that  of  the  solution  of  salt  underneath — is  a 
cause  assigned  for  the  folding  and  faulting  of  overlying  limestones  in 
central  New  York.  Wheelock  attributes  a  series  of  faults  in  the  Scalaris 
and  Helderberg  limestones  to  the  solution  of  salt  in  the  Salina  formation 
beneath  them.  His  explanation  is  as  follows: 

As  the  rocks  of  central  New  York  dip  slightly  toward  the  south,  the 
hypothenuse  of  the  triangle  would  be  shortened  by  the  dropping  down  of  the 
overlying  formation  due  to  the  solution  of  the  salt,  and  thus  produce  a  lateral 
pressure  in  the  rocks  capable  of  causing  overthrusts.1 

In  a  summary  of  the  thrust  faults  of  central  New  York,  P.  F.  Schneider 
says: 

Inasmuch  as  most  of  the  above  mentioned  disturbances  occur  in  or  near 
the  Helderberg  escarpment,  composed  in  the  main  of  heavy  limestones  aggre- 
gating several  hundred  feet  in  thickness,  and  the  persistence  of  the  faults 
across  central  New  York,  it  would  seem  that  all  are  the  result  of  some  con- 
siderable force  capable  of  affecting  this  entire  region.  In  a  general  way  the 
solution  of  salt  from  the  Salina  formation  which  immediately  underlies  the 
Helderberg  series  has  been  regarded  as  an  explanation  for  all  the  disturbance 
of  this  region.2 

Though  suggesting  other  possible  causes  for  the  deformation,  he  repeats 
Wheelock's  idea, 

that  from  solution  any  settling  of  the  layers  must  shorten  the  length  of  the 
hypothenuse  of  the  triangle,  and  thus  produce  the  force  which  crumpled  and 
fractured  the  rocks. 

Of  the  faults  mentioned  by  Wheelock,  occurring  in  central  New 
York  from  Little  Falls  to  Ithaca,  those  in  the  northeastern  part  of  the 
area  mentioned  need  not  be  considered  as  resulting  from  solution  of  the 
Salina,  as  they  are  in  the  older  formations,  the  Salina  having  been 
eroded  back  far  to  the  southwest.  As  to  the  shortening  of  the  hypothe- 
nuse on  the  monocline  by  solution  of  the  salt  beneath,  it  may  not  be 
irrelevant  to  inquire  whether  shortening  of  sufficient  amount  would 
take  place  to  produce  any  such  deformation  as  is  recorded  in  the  central 

1  C.  E.  Wheelock,  Science,  New  Sen,  XXII  (1905),  673. 

2  P.  F.  Schneider,  Amer.  Jour.  Set.,  4th  Ser.,  XX  (1905),  308-12. 


56  STUDIES  IN  MINOR  FOLDS 

New  York  area.  P.  F.  Schneider1  has  listed  a  number  of  these  faults, 
giving  the  amount  of  displacement  for  them  as  15,  3,  3,  2,  4,  42,  and 
6  feet,  or  a  total  for  those  described  of  75  feet. 

In  regard  to  the  shortening  of  the  hypothenuse  as  a  cause  for  defor- 
mation, it  may  be  noted  that  most  of  the  faulting  and  folding  is  back 
about  13  miles  south  of  the  exposure  of  the  top  of  the  Salina  formation. 
The  general  southward  dip  in  Onondaga  County  is  given  as  40  feet  per 
mile.2  However,  if  one  figures  the  fall  of  the  Salina  from  its  outcrop  at 
400  feet  A.T.  north  of  Syracuse,  to  the  Solway  Company  Well  No.  30 
near  Tully,  there  is  a  drop  of  741  feet  in  25  miles,  or  a  trifle  less  than 
30  feet  per  mile.3  Using  the  larger  figure  of  40  feet  per  mile  for  13  miles, 
the  distance  from  the  outcrop  to  the  region  of  the  deformation,  there 
would  be  a  fall  of  520  feet.  Solution  for  the  hypothenuse  shows  it  is 
less  than  2  feet  longer  than  the  bottom  leg.  It  is  seen  then  that  if 
there  were  sufficient  solution  to  drop  the  hypothenuse  the  entire  520  feet, 
there  would  be  shortening  of  less  than  2  feet  to  account  for  the  defor- 
mation noted  above.  This  is  entirely  inadequate.  Furthermore,  the 
thickness  of  soluble  beds  is  not  sufficient  to  allow  a  settling  to  the  extent 
of  520  feet. 

The  thickness  given  by  Luther  for  the  salt  beds  of  the  region  is 
variable,  being  180,  214,  220,  and  318  feet  at  different  places.4  If  to 
the  largest  figure,  318  feet,  we  add  the  thickness  of  the  gypsum-bearing 
shales,  115  feet,  there  is  still  less  than  the  length  of  the  opposite  leg  of 
the  triangle  noted  above.  This  would  still  further  reduce  the  amount 
of  thrust  faulting  possible  from  this  cause. 

It  is  indicated  then  that  if  the  salt  and  gypsum,  equal  in  amount  to 
that  now  found  13  miles  south  of  the  outcrop  of  the  Salina  formation, 
had  dissolved  from  beneath  the  overlying  formations,  the  shortening  of 
the  hypothenuse  for  the  area  would  have  been  far  too  slight  to  account 
for  the  deformation  which  has  taken  place.  The  fact  that  older  forma- 
tions in  the  northeastern  part  of  the  area  have  been  affected  is  suggestive 
that  where  those  older  formations  go  beneath  the  Salina  they  may  there 
also  be  affected,  indicating  that  the  faults  and  folds  of  central  New  York, 
like  those  farther  northeast,  represent  deep-seated  movements  of  a  real 
tectonic  character. 

1  P.  F.  Schneider,  Amer.  Jour.  Sci.,  4th  Ser.,  XX  (1905),  308-12. 

*  D.  D.  Luther,  "Geol.  Onondaga  Co.,"  N.Y.  State  GeoL  Kept.  (1895),  p.  272. 

3  D.  D.  Luther,  ibid.,  pp.  255,  256. 

4  D.  D.  Luther,  ibid. 


STUDIES  IN  MINOR  FOLDS  57 

Still  another  point  to  be  considered  is  the  nature  of  the  movement 
that  would  take  place  as  a  result  of  solution  in  a  lower  one  of  a  series 
of  beds  on  a  gently  dipping  monocline.  If  solution  is  most  rapid  at 
and  just  below  the  outcrop  of  the  soluble  formation,  as  solution  takes 
place,  a  slow  settling  of  the  edge  of  the  next  higher  formation  would 
result.  As  solution  increased  at  points  farther  down  the  dip,  the  settling 
of  the  formation  above  would  be  correspondingly  shifted  down  the  dip. 
Now  if  there  be  a  lateral  shortening  of  only  i  or  2  feet  in  a  distance  of 
from  10  to  15  miles,  this  movement  is  more  likely  to  be  taken  up  between 
the  beds  and  in  the  weak  intermediate  formations  than  to  break  with 
marked  thrusts  across  the  heavy  bedded  limestones,  or  throw  them  into 
distinct  folds. 

It  is  believed  that  in  the  area  under  consideration,  to  the  west  of 
the  central  New  York  region,  the  folds  and  faults  are  not  due  to  solution 
of  salt  and  gypsum.  In  fact,  the  deep  well  at  Erie  shows  no  rock  salt, 
but  some  gypsum  mixed  with  marl  at  a  depth  of  from  1,700  to  1,815 
feet.1  Thus  the  absence  of  salt,  and  the  slight  amount  of  deformation 
possible  as  a  result  of  the  solution  of  beds  beneath,  point  to  something 
other  than  solution  as  a  cause  for  the  folds  and  faults.2 

Faulting  due  to  compacting  of  soft  rocks. — It  would  seem  that  the 
conditions  favoring  the  accumulation  of  tangential  stresses  of  sufficient 
intensity  to  fold  or  overthrust  rocks  would  be  present,  because  of  the 
compacting  of  softer  sediments,  only  when  highly  compressible  sedi- 
ments for  a  region  were  overlain  by  well-compacted  and  more  rigid 
rocks.  If  compacting  over  a  large  area  should  result  in  extensive 
shrinkage  of  an  underlying  formation,  the  settling  of  the  superjacent 
formations  would  result  in  radial  shortening.  Any  considerable  radial 
shortening  for  a  large  area  would  initiate  lateral  stresses  competent  to 
fold  and  fault  the  rocks.  If,  however,  the  shrinkage  is  irregular,  and 
limited  to  small  areas,  the  question  of  adequacy  arises.  The  arc  of  the 
circle  is  so  large  and  flat  that  a  slight  amount  of  shrinkage  over  a  small 
area  would  not  have  much  effect  in  producing  lateral  stresses.  G.  S. 
Rogers3  has  given  this  compacting  as  a  possible  cause  for  a  small  fault 
which  he  has  found  in  a  coal  bed  in  southeastern  Montana,  not  far  from 
the  confluence  of  the  Big  Horn  and  Yellowstone  rivers.  It  is  in  the 

1  G.  S.  Prosser,  Geol.  Stirv.  Ohio  Bull.  15,  4th  Ser.  (1912),  p.  414. 

2  More  recent  experience  of  the  writer  in  the  region  of  gypsum-bearing  rocks  of 
southwestern  Kansas  has  shown  that  folds  and  faults  due  to  solution  of  gypsum  differ 
greatly  in  character  from  those  in  the  Great  Lakes  region. 

3  G.  S.  Rogers,  Jour.  Geol.,  XXI  (1913),  534-36. 


58  STUDIES  IN  MINOR  FOLDS 

midst  of  generally  flat-lying  strata  about  70  miles  from  the  Big  Horn 
Mountains.  The  thrust  is  slight,  with  a  displacement  of  only  29  inches. 
The  form  of  the  fault  is  peculiar  in  that  the  upthrown  side  is  vertical  for 
a  distance  of  about  2  feet,  and  then  is  turned  in  a  horizontal  position  at 
the  top,  or  practically  at  right  angles  to  the  lower  part  of  the  upthrust, 
as  though  two  forces  differing  in  direction  had  affected  it  successively. 
Both  the  character  and  the  competency  of  the  overlying  beds  would 
have  some  influence  in  determining  the  manner  in  which  superjacent 
beds  would  be  affected  by  local  compacting  and  shrinkage  of  the  under- 
lying strata.  H.  F.  Bain1  considers  the  irregular  shrinkage  in  the  "oil 
rock"  at  the  base  of  the  Galena  dolomite  as  the  cause  of  the  flats  and 
pitches  in  the  lower  part  of  that  formation;  the  idea  being  that  con- 
siderable local  shrinkage  gave  opportunity  for  the  opening  of  spaces 
between  the  beds,  and  caused  diagonal  breaks  across  them  analogous 
to  the  openings  found  in  a  brick  or  stone  wall  when  a  window  or  door 
frame  gives  beneath  the  masonry  above.  But  in  this  case  no  folds  or 
faults  resulted  in  the  rocks  superjacent  to  those  which  were  compressed. 
The  compacting  of  beds  by  weight  of  overlying  strata  doubtless  is  wide- 
spread, and  when  the  superjacent  beds  are  rigid  because  of  crystallinity 
or  other  cause,  movements  necessary  to  accommodate  them  to  the  new 
positions  they  may  take  as  a  result  of  shrinkage,  cannot  be  accom- 
plished without  considerable  lateral  movement.  Accordingly,  lateral 
stresses  will  be  set  up,  for  the  result  will  be  that  of  radial  shortening. 
If  there  be  real  radial  shortening,  there  will  be  cause  for  tangential 
thrust  in  the  ratio  of  about  i  to  6  for  the  entire  earth,2  or  for  an  approxi- 
mate circumference  of  24,000  miles.  So  for  the  entire  earth,  100  feet  of 
radial  shortening  would  give  600  feet  of  thrust.  For  a  lo-mile  arc 
100  feet  of  radial  shortening  would  give  -^Vo  °f  600  or  J  foot,  and  for  a 
2-mile  arc,  100  feet  of  radial  shortening  would  give  -£v  of  a  foot.  Two 
folds  with  associated  faults  along  Paine  Creek  have  the  crustal  shorten- 
ing of  7  feet  8  inches  within  2  miles.  Xhe  ratio  for  the  thrust  here 
because  of  the  shortening  would  be  i :  ^oVfr>  or  to  get  a  shortening  of  one 
foot  there  would  be  2,000  feet  of  depression.  But  possibly  these  defor- 
mations relieved  stresses  for  a  mile  either  side  of  the  folds,  so  we  should 
consider  the  distance  for  the  shortening  for  4  miles  instead  of  two.  Even 
for  4  miles  there  would  need  to  be  a  depression  of  1,000  feet  to  cause 
i  foot  of  thrust.  Along  Elk  Creek,  south  of  Girard,  over  n  feet  of 
shortening  has  occurred  within  a  mile.  The  7  faults  farther  east  in 

1  H.  F.  Bain,  U.S.  Geol.  Surv.  Bull.  294  (1906),  p.  44. 

2  T.  C.  Chamberlin  and  R.  D.  Salisbury,  Geology,  I  (1905),  580. 


STUDIES  IN  MINOR  FOLDS  59 

central  New  York,  as  noted  above,  have  a  total  displacement  of  75  feet, 
and  these  occur  within  an  arc  of  10  miles.  The  displacements  in  the 
eastern  area  should  not  be  added,  for  they  occur  in  four  different  locali- 
ties, Marcellus,  East  Onondaga,  Jamesville,  and  Manlius,  almost  in  an 
east-and-west  line.  As  the  shortening  is  a  north-and-south  one,  they 
probably  represent  a  continued  deformation.  But  a  single  displace- 
ment at  East  Onondaga  is  42  feet,  one  at  Jamesville  15  feet,  and  four 
others  12  feet.  If  depression  here  has  taken  place  over  an  arc  10  miles 
across,  the  ratio  would  be  i :  TJ- Q-,  or  there  would  be  a  settling  of  400  feet 
to  i  foot  of  thrust.  So  to  get  42  feet  of  thrust  a  depression  of  16,800  feet 
would  be  required.  Also,  the  shortening  noted  above  does  not  include 
several  folds  that  occur  in  the  general  region  with  the  faults.  Thus  from 
a  quantitative  standpoint  the  shortening  of  the  arc  of  a  segment  due  to 
settling  from  compacting  of  subjacent  rocks,  is  far  too  small  to  cause 
thrusts  of  even  the  small  magnitude  of  those  in  the  Lake  Erie  region  or 
in  central  New  York. 

Vertical  pressure  of  valley  walls. — W.  O.  Crosby1  is  credited  with 
having  suggested  the  weight  of  the  overlying  strata  as  an  explanation 
for  the  marked  small  folds  at  Trenton  Falls,  New  York,  but  W.  J. 
Miller  concludes  that  the  overturned  folds  cannot  be  accounted  for  in 
this  way.  Smallwood  and  Hopkins,  in  their  discussion  of  the  origin  of 
the  folds  near  Meadville,  consider  the  possibility  of  the  weight  of  the 
valley  walls  being  sufficient  to  deform  the  rocks  in  the  bottoms  of  the 
valleys,  but  conclude  that  they  are  not  sufficiently  high  to  develop  an 
adequate  force.2  This  conclusion  seems  well  founded,  for  the  walls  of 
the  deepest  sharp  post-glacial  valleys  in  the  vicinity  of  Meadville  reach 
scarcely  100  feet  in  height.  Sandy  shales  and  some  sandstones,  as  well 
as  the  argillaceous  shales,  are  involved  in  the  folds  there.  The  deepest 
valley  on  the  southern  border  of  Lake  Erie,  near  Westfield,  New  York, 
is  400  feet  deep.  Figuring  165  pounds  per  cubic  foot  for  the  shales  and 
sandstones  in  the  walls  of  these  valleys,  there  would  be  only  about  460 
pounds  pressure  per  square  inch  on  the  rocks  at  the  bottom  of  the  valleys 
beneath  the  walls  400  feet  high,  and  115  pounds  on  those  with  walls  of 
100  feet.  The  crushing  strength  of  the  weaker  sandstones  can  hardly 
be  lower  than  1,500  pounds  per  square  inch.3  This  is  far  above  either 

*W.  O.  Crosby,  Jour.  Geol.,  XVI  (1908),  430;  and  Man.  N.Y.  Acad.  Sci.,  XV 
(1895-96),  90. 

2  Smallwood  and  Hopkins,  Bull.  Syracuse  Univ.,  4th  Ser.,  No.  i  (1903),  pp.  18-24. 
s  L.  V.  Pirsson,  Rocks  and  Rock  Minerals  (1915),  p.  324. 


60  STUDIES  IN  MINOR  FOLDS 

figure  for  the  pressure  due  to  the  weight  of  rocks  in  the  walls  of  the 
valleys.  It  is  significant,  too,  that  most  of  the  smaller  folds  of  the  area, 
occurring  in  the  floors  of  valleys  parallel  to  the  walls,  are  found  in  those 
with  relatively  low  walls  of  about  100  feet  or  less. 

G.  F.  Becker  has  given  an  excellent  summary  of  the  rupturing  effect 
of  stress  due  to  gravity  as  follows: 

When  gravity  acts  on  a  mass,  homogeneous  strain  is,  strictly  speaking, 
impossible,  excepting  within  infinitesimal  limits  of  space,  each  level  surface 
being  subjected  to  greater  pressure  than  the  next  above  it.  On  the  other 
hand,  the  forces  involved  in  the  deformation  and  fracture  of  rocks  are  very 
great,  except  in  some  extreme  instances,  such  as  that  of  moist  clay.  For 
ordinary  firm  rocks  the  ultimate  strength  is  such  that  a  column  of  from  one 
to  several  thousand  feet  in  height  would  be  needful  to  produce  at  its  base  a 
pressure  sufficient  to  produce  rupture.  Consequently  in  masses  of  such 
material  from  a  few  score  of  feet  to  a  few  hundred  feet  in  thickness,  gravity 
plays  but  a  small  part  compared  with  the  rupturing  stress.1 

His  conclusions  are  in  conformity  with  the  figures  above,  showing  that 
the  weight  of  these  valley  walls  is  far  below  that  necessary  to  rupture 
solid  rocks. 

Folds  due  to  relief  from  compression. — Folds  occurring  in  the  quarries 
or  valleys  frequently  are  attributed  to  relief  of  pressure  by  the  removal 
of  rock  from  above.  Such  an  explanation  has  been  given  for  a  small 
anticline  in  the  Queenston  shale  at  the  head  of  Hopkins  Creek  estuary, 
south  of  Lake  Ontario,  of  which  it  is  said:  "It  probably  is  a  secondary 
result  of  erosion,  the  removal  of  the  overlying  rocks  permitting  relief 
from  compression."2  But  relief  from  vertical  compression  alone  could 
have  nothing  to  do  with  the  formation  of  folds.  If  marked  stresses 
already  exist  in  the  rocks,  and  the  superficial  strata  by  their  strength 
and  weight  prevent  folding,  then  their  removal  might  permit  the  stresses 
resident  in  the  subjacent  weaker  rocks  to  become  effective  by  throwing 
those  weaker  rocks  into  folds. 

Folds  due  to  weight  of  delta. — In  several  places  in  the  western  part 
of  the  United  States,  folds  occur  at  the  base  of  large  deltas.  I.  C.  Russell 
has  described  and  figured  folds  which  occur  at  the  base  of  the  Provo 
delta,  along  the  Logan  River,  Utah.  He  suggests  as  an  explanation  of 
the  folds,  that  the  weight  of  300  feet  of  delta  material  pressed  out  some 
of  the  soft,  freshly  deposited  sediments  and  arched  them  up  into  a  series 
of  folds,  developing  the  folds  of  the  series  successively  as  it  was  built 

1  G.  F.  Becker,  Bull.  Geol.  Soc.  Amer.,  IV  (1893),  49-50. 
3  Niagara  Folio,  No.  190  (1913),  p.  15. 


STUDIES  IN  MINOR  FOLDS  61 

forward.  He  computes  the  difference  between  weight  of  water  and 
weight  of  delta  as  75  pounds  per  square  inch.1  Russell  thinks  the  folds 
in  the  lower  part  of  deltas  in  Lake  Lahontan,  Utah,  and  in  the  Mono 
Valley,  California,  also  are  due  to  the  weight  of  deltas.2 

The  deformation  of  soft,  unindurated  sediments  by  the  weight  of  a 
thick  delta  deposit  seems  very  possible,  but  a  similar  weight  would  have 
little  effect  on  indurated  shales  and  sandstones  such  as  are  folded  and 
faulted  in  the  Lake  Erie  region.  Besides,  no  deltas  of  the  type  and  mag- 
nitude described  by  Russell  are  found  in  this  area. 

Deformation  due  to  landslides. — Numerous  small  anticlines  occur  in 
the  bottom  of  post-glacial  valleys  in  the  vicinity  of  Meadville  and  in 
the  tributaries  of  Walnut  Creek,  south  of  Erie.  The  valleys  are  narrow 
at  the  bottom  and  have  steep  sides.  Generally  the  folds  are  about 
parallel  with  the  trend  of  the  valley.  Some  of  these  folds  are  asso- 
ciated with  landslides,  and  W.  M.  Smallwood  and  T.  C.  Hopkins  at- 
tribute the  formation  of  the  folds  largely,  if  not  entirely,  to  this  cause.3 
However,  many  of  the  folds  are  in  no  way  related  to  landslides,  and 
numerous  large  landslides  have  caused  no  deformation  of  the  strata. 
As  the  height  of  the  valley  walls  is  generally  less  than  100  feet,  the 
force  from  the  slow  settling  of  a  comparatively  small  landslide  down  a 
45°  slope,  is  thought  to  be  entirely  inadequate  to  deform  8  to  20  feet  of 
well-indurated  shales  and  sandstones  commonly  involved  in  the  folds  in 
the  valley  floors.  R.  T.  Chamberlin4  has  noted  much  larger  folds  of 
this  type  in  materials  of  the  slides  along  Lakes  Zug  and  Zurich  in  Switzer- 
land, where  the  rocks  beneath  the  slide  were  undisturbed. 

A  few  of  these  folds,  particularly  some  in  the  sharp  southern  tribu- 
taries of  Walnut  Creek,  before  referred  to,  not  only  are  related  to  land- 
slides, but  clearly  are  a  part  of  them.  In  at  least  two  instances  the 
landslides  were  forced  across  the  narrow  floor  of  the  valleys,  and  the 
strata  in  the  lower  part  of  the  slide  were  buckled  into  anticlinal  form 
by  the  weight  of  the  upper  part  of  the  slide.  It  would,  however,  take 
far  less  force  to  buckle  up  in  the  end  of  a  slide  the  strata  which  have 
been  loosened  by  the  movement,  than  would  be  required  to  deform  the 
undisturbed  bedrock  of  the  valley  floor. 

Should  there  be  a  prominent  joint  in  the  rock  a  short  distance  back 
in  the  valley  wall  about  parallel  with  the  trend  of  the  valley,  cutting 

1  Credited  to  I.  C.  Russell  by  G.  K.  Gilbert,  U.S.G.S.  Mono.,  I  (1890),  162. 
2 1.  C.  Russell,  Eighth  Ann.  Kept.  U.S.G.S.,  Part  i  (1886-87),  p.  310. 

3  Smallwood  and  Hopkins,  Bull.  Syracuse  Univ.,  4th  Ser.,  No.  i  (1903),  pp.  18-24. 

4  Unpublished  correspondence. 


62  STUDIES  IN  MINOR  FOLDS 

beneath  the  edge  of  the  valley  floor  and  sloping  steeply  in  the  wall,  it 
might  determine  the  plane  of  a  break  in  the  wall.  Should  a  large  mass 
of  rock  with  broad  top  rest  on  a  relatively  small  base,  the  pressure  on 
that  base  would  be  greatly  increased,  and  might  cause  the  surface 
layers  of  a  weak  rock  to  buckle  in  the  bottom  of  the  valley  in  front  of  it. 
It  may  be  well  to  inquire,  in  this  connection,  whether  it  is  possible  for 
folding  in  a  valley  floor  to  initiate  landslides.  If,  because  of  lateral 
stresses,  the  rocks  fold  up  in  the  valley  floor,  there  might  be  a  slight  giv- 
ing under  the  edge  of  the  valley  in  a  way  to  loosen  the  strata  above  and 
cause  a  landslide. 

The  illustration  of  a  fold  at  the  base  of  a  cliff  antedating  a  slide  is 
given  by  F.  R.  Van  Horn.1  It  is  in  the  quarry  of  the  Cleveland  Brick 
and  Clay  Company,  along  Mill  Creek,  at  Cleveland.  Back  a  distance 
from  the  edge  at  the  top  of  the  quarry  wall,  which  is  112  feet  high,  a 
fissure  opened  August  17,  1908.  The  following  day  a  small  anticline 
200  feet  long,  started  to  buckle  up  at  the  base  of  the  bank,  in  the  shales 
weakened  by  the  blasting.  The  day  following  the  initiation  of  the 
buckling,  the  mass  of  rock,  estimated  to  weigh  87,732  tons,  started  to 
settle.  It  was  stated  definitely  by  the  quarryman,  who  watched  the 
phenomena,  that  the  buckling  preceded  any  settling  of  the  mass.  After 
the  settling  began,  it  continued  at  the  slow  rate  of  6  feet  in  two  weeks, 
and  of  20  feet  in  a  little  over  four  months.  After  the  excavation  of 
most  of  the  shale  of  the  slide,  it  appeared  that  a  joint  crack  had  reached 
up  80  feet  of  the  112  in  the  quarry  wall,  this  crack  having  determined 
the  location  of  the  fissure  at  the  top  of  the  bank.  If  this  joint  crack 
extended  a  short  distance  below  the  floor  of  the  quarry,  the  identical 
conditions  exist  which  are  postulated  with  reference  to  the  valley  wall 
in  a  landslide  described  above.  In  this  instance  the  slide  and  the  small 
fold  parallel  with  its  front  seem  definitely  related.  The  amount  of 
weakening  by  the  shattering  of  the  shales  in  the  base  of  the  high  bank  and 
on  the  quarry  floor  is  not  known,  but  it  may  have  been  very  considerable. 

Another  consideration  to  be  noted  in  connection  with  folds  related 
to  landslides,  both  in  this  quarry  and  in  the  valleys  in  the  area  studied, 
is  that  lateral  stresses  of  importance  may  already  exist  in  the  rocks.  If 
such  stresses  do  exist,  and  to  them  are  added  the  relatively  smaller 
ones  initiated  by  the  landslides,  the  combined  stresses  are  then  suffi- 
cient to  overcome  the  strength  of  the  rocks  and  bow  them  up.  In  this 
case,  while  definite  stresses  are  added  by  action  of  the  landslide,  their 
minor  force  may  be  looked  upon  as  a  trigger  which  has  added  its  slight 

1  F.  R.  Van  Horn,  Bull.  Geol.  Soc.  Amer.,  XX  (1908),  625-32. 


STUDIES  IN  MINOR  FOLDS  63 

power  to  the  larger  forces  it  sets  in  motion.  Reasons  for  thinking  that 
such  lateral  stresses  exist  in  the  rocks  of  the  area  studied  will  be  given  later. 

Pressure  of  natural  gas. — In  this  area  gas  occurs  under  low  pressure 
at  an  average  depth  of  600  feet.  At  one  locality  it  is  constantly  escap- 
ing from  the  crest  of  the  anticline  shown  in  Figure  38.  I.  C.  White1 
has  attributed  the  " minute  cracked  anticlines"  of  the  area  to  the  pres- 
sure of  natural  gas.  However,  the  wells  produce  little  gas,  and  that 
little  under  low  pressure.  Furthermore,  the  folds  occur  both  within 
and  without  the  areas  productive  of  gas.  While  the  pressure  of  natural  gas 
clearly  produces  stresses,  it  is  thought  that  they  are  far  too  weak,  with 
the  low  pressures  common  here,  to  deform  the  rocks.  Besides,  the 
release  of  strains  due  to  gas  pressure  doubtless  would  come  in  the  forma- 
tion of  domes  and  symmetrical  folds  rather  than  in  the  markedly  unsym- 
metrical  ones  common  in  the  area  under  consideration. 

Differential  movements. — W.  J.  Miller2  has  suggested  that  differ- 
ential movement  in  the  mass  of  the  Trenton  limestone,  in  the  large  fault 
at  Prospect  Village  near  Trenton  Falls,  New  York,  has  caused  the  folds 
in  two  horizons  which  lie  between  unfolded  strata.  The  suggestion  is 
excellent,  and  it  seems  probable  that  as  the  end  of  the  upthrown  part  of 
the  fault  has  been  greatly  eroded,  these  small  folds  are  the  best  existing 
index  of  the  amount  and  character  of  the  lateral  movement  in  the  fault. 
In  several  instances  in  the  area  studied  only  a  few  feet  of  the  superficial 
rocks  seem  to  be  involved  in  the  folds.  In  these  few  cases  the  beds 
underneath  are  undisturbed,  while  the  more  superficial  ones  are  deformed, 
thus  seeming  to  indicate  either  more  acute  stresses  or  greater  weakness 
in  the  upper  than  in  the  lower  rocks.  But  these  very  superficial  folds 
seem  to  be  in  no  way  related  to  a  larger  fault.  In  many  of  the  folds, 
however,  the  deformation  appears  to  involve  the  rocks  to  a  considerable 
depth  as  well  as  the  superficial  ones,  but  none  are  related  to  a  large  fault. 

Glaciation. — Many  folds  of  varying  types  and  magnitude  have  been 
attributed  to  the  action  of  glaciers.  Glaciation  has  been  so  much  abused 
in  having  unreasonable  destructive  and  deformative  acts  attributed  to  it, 
that  the  prevailing  tendency  now  is  to  scrutinize  with  care  the  charge 
"due  to  glaciation."  The  real  deformation  of  rock  which  may  rightly 
be  attributed  to  glacial  action  is  now  thought  to  be  very  moderate. 
The  work  attributed  to  glaciation  by  J.  A.  Udden3  and  F.  W.  Sardeson4 

1 1.  C.  White,  Second  Geol.  Surv.  Pa.,  Kept.  Q<  (1881),  p.  120. 

2  W.  J.  Miller,  Jour.  Geol.,  XVI  (1908),  428-33. 

3  J.  A.  Udden,  III.  Geol.  Surv.  Bull.  8  (1908),  pp.  255-67. 

4  F.  W.  Sardeson,  Jour.  Geol.,  XIII  (1903),  351-57. 


64  STUDIES  IN  MINOR  FOLDS 

seems  excessive.  Udden  describes  and  illustrates  many  small  folds  and 
faults  in  the  walls  of  valleys  and  in  coal  mines,  some  of  the  faults  having 
a  displacement  of  30  to  100  feet.  He  thinks  the  folds  and  faults  near 
Peoria,  Illinois, 

are  disturbances  in  the  upper  part  of  the  soft  bed  rock,  caused  by  the  pres- 
sure and  motion  of  a  continental  ice  sheet  in  the  Pleistocene  period;  that  they 
are  planes  marking  the  outline  of  immense  blocks  of  large  tracts  of  the  upper- 
most coal  measure  strata  covering  probably  hundreds  of  acres  of  land  which 
have  been  dislodged  from  their  position,  displaced,  fractured,  rotated  hori- 
zontally and  at  times  vertically,  and  partly  ground  to  till.1 

Sardeson  speaks  of  glaciers  "plowing  up  bed  rock,"2  and  transmitting 
stresses  through  beds  of  gravel  and  till  16  to  20  feet  in  thickness,  over 
which  they  are  moving  with  such  efficiency  as  to  fold  and  overthrust 
the  Galena  limestone  beneath  the  gravel  and  drift. 

E.  M.  Kindle  and  F.  B.  Taylor3  have  described  and  illustrated  an 
anticline  at  Thirty  Mile  Point,  along  the  southern  shore  of  Lake  Ontario 
just  east  of  the  Niagara  quadrangle,  and  they  attribute  the  origin  to  the 
pressure  of  glacial  ice,  in  spite  of  the  fact  that  it  is  overturned  into 
the  glacial  till  and  includes  till  definitely  beneath  the  overturned  top  of  the 
fold.  In  G.  K.  Gilbert's4  earlier  description  of  this  fold  he  advances 
two  hypotheses  for  its  origin,  but  does  not  conclude  definitely  as  to 
either  one.  If  due  to  glaciation  his  idea  is  that  the  waning  ice  stopped 
just  north  of  this,  then  moved  forward  again  enough  to  form  the  fold 
and  overturn  it  into  the  drift.  The  shore  has  undoubtedly  been  eroded 
back  a  long  distance  in  the  sandy  shale  at  this  locality,  possibly  a  mile  or 
more.  If  the  glacier  moved  forward  several  times  over  the  area,  it 
seems  strange  that  it  should  wait  until  a  last  slight  advance  to  deform 
the  rocks. 

J.  Le  Conte  attributes  folds  in  several  horizons  in  clays  along  Rush 
Creek,  in  the  Mono  Valley,  California,  to  glaciers  or  icebergs,5  but 
I.  C.  Russell  determined  that  the  glaciers  did  not  come  within  3  miles 
of  the  area  described,  and  that  the  folds  were  so  widespread,  and  many 
of  them  of  such  a  nature,  that  they  could  not  have  been  formed  by 
icebergs.6 

1  J.  A.  Udden,  op.  cit.,  p.  265. 

2  F.  W.  Sardeson,  op.  cit.,  p.  356. 

3  Kindle  and  Taylor,  Niagara  Folio  (1913),  p.  15,  and  Plate  19. 
*  G.  K.  Gilbert,  Bull.  Geol.  Soc.  Amer.,  X  (1898),  131. 

5  J.  Le  Conte,  Amer.  Jour.  Sci.,  3d  Ser.,  XVIII  (1897),  40- 

6 1.  C.  Russell,  Eighth  Ann.  Kept.  U.S.G.S.,  Part  i  (1889),  p.  309. 


STUDIES  IN  MINOR  FOLDS  65 

There  are  but  two  localities  in  the  area  studied  in  which  folds  of 
such  a  character  were  found  that  their  origin  could  be  attributed  to 
glacial  pressure.  One  was  in  an  open-pit  coal  mine  5  miles  south  of 
Conneautville,  Pennsylvania,  and  the  other  in  shales  along  Canadaway 
Creek  ij  miles  west  of  Dunkirk,  New  York.  In  both  instances  the 
topographic  situation,  presenting  a  steep  slope  toward  the  north,  the 
general  direction  from  which  the  ice  came,  favored  the  transmission  of 
stress  into  the  coal  in  one  case  and  the  shale  in  the  other,  as  the  ice 
advanced  against  these  transverse  barriers.  In  both  instances  the  folds 
are  small,  only  a  few  feet  of  strata  being  involved,  and  the  rocks  much 
broken,  indicating  that  the  folding  took  place  without  much  pressure 
from  above.  The  two  small  folds  in  the  coal  are  shown  in  Figure  35, 
and  being  indistinct  they  are  outlined  by  the  dotted  line.  The  hammer 
is  i  if  inches  long.  About  6  feet  of  broken  and  crushed  coal  lie  above 
the  folds,  and  a  few  feet  to  the  right  of  them,  toward  the  north,  the 
glacial  till  is  intermingled  with  the  broken  coal.  The  coal  at  the  top  of 
the  hill  is  an  outlier  of  a  more  extensive  formation  to  the  south.  Appar- 
ently the  ice,  advancing  against  the  steep  northern  slope  of  the  hill, 
shattered  and  slightly  deformed  the  northern  end  of  the  coal  vein  before 
it  was  deflected  above  the  top  of  the  hill.  The  folds  in  the  Dunkirk 
shale  of  the  Portage  group,  near  Dunkirk,  are  shown  in  Figure  36. 
Three  small  anticlines  occur  in  the  series,  and  each  is  about  10  feet  wide. 
The  sandstones  beneath  the  shales  are  undisturbed.  The  thickness  of 
the  shale  is  5  feet,  and  it  is  overlain  by  3  feet  of  glacial  drift  and  soil. 
A  short  distance  to  the  north  of  the  folds  the  shale  presents  an  abrupt 
slope  to  the  north. 

Because  of  the  topographic  situation  with  reference  to  the  advancing 
ice  front  these  very  small  folds  in  coal  and  shale  seem  readily  attributable 
to  the  pressure  of  glacial  ice.  The  fact  that  larger  folds  due  to  glacial 
pressure  were  not  found  in  this  area  does  not  constitute  proof  that  they 
do  not  occur  elsewhere.  It  is  thought,  however,  that  this  extremely 
minor  type  of  folding  is  all  that  can  be  expected  from  the  glacial  ice 
pressure,  because  of  its  softness,  and  plastic  adjustment  under  com- 
pression. 

A  detailed  study  of  the  major  and  minor  deflections  of  the  ice  due  to 
various  types  of  barriers  would  be  instructive  in  this  connection,  but  it 
cannot  be  followed  here.  Brief  attention  is  called  to  the  plastic  adjust- 
ment of  the  ice  under  pressure  as  indicated  by  the  manner  in  which  it 
fitted  into  the  irregularities  of  the  rock  surface.  An  illustration  of  this 
adjustment  is  seen  in  the  south  quarry  at  Stony  Island,  in  Chicago, 


66 


STUDIES  IN  MINOR  FOLDS 


where  the  underside  of  a  small  projecting  ledge  of  the  Niagara  limestone 
has  been  polished  by  the  wear  of  the  ice  and  its  tools.     In  another 


FIG.  35. — Two  small  folds  in  the  north  edge  of  an  open  coal  mine.     The  hammer 
is  ii f  inches  long.     Five  miles  south  of  Conneaut  Lake,  Pa. 


FIG.  36. — Small  folds  in  5  feet  of  Dunkirk  shales  i^  miles  west  of  Dunkirk,  N.Y. 
The  thick  homogeneous  beds  are  outlined  by  the  dotted  lines. 

locality,  on  Kelly's  Island,  in  the  western  part  of  Lake  Erie,  the  ice  was 
forced  with  great  pressure  through  the  sinuosities  of  a  tortuous  channel 
without  breaking  off  the  interlocking  spurs  of  the  rock.1 

TT.  C.  Chamberlin  and  R.  D.  Salisbury,  Geology,  III  (1906),  349,  Fig.  485. 


STUDIES  IN  MINOR  FOLDS  67 

Drag  of  icebergs. — In  a  few  instances  folds  in  unconsolidated  clays 
and  sands  have  been  attributed  to  the  drag  of  icebergs  over  them.  J.  Le 
Conte1  has  suggested  that  explanation  for  the  folds  in  the  clays  and 
sands  in  the  beds  deposited  in  Lake  Mono.  A  like  cause  has  been 
credited  by  R.  D.  Salisbury  and  W.  W.  Atwood2  with  the  deformation 
of  layers  of  sand  and  silt  in  the  glacial  lake  deposit  in  the  Baraboo  region 
of  Wisconsin.  I.  C.  Russell3  questions  the  possibility  of  any  type  of  ice 
origin  for  the  folds  in  the  former  case,  but  it  seems  quite  possible  that 
local,  narrow,  irregular  areas  of  unconsolidated  sediments  might  be  so 
deformed.  If  the  grounding  and  drag  of  icebergs  have  caused  the  defor- 
mation of  lake  beds,  the  general  direction  of  the  current  from  the  ice  front 
to  the  outlet  of  the  lake  would  indicate  the  course  of  the  icebergs,  and  the 
axes  of  the  folds  would  be  about  normal  to  the  direction  of  their  course. 

Tangential  compression. — The  closed  folds  and  thrust  faults  of  the 
Taconic,  Appalachian,  Ouachita,  Arbuckle,  and  Wichita  mountains  give 
evidence  that  stresses  of  great  potency  of  a  tangential  nature  have  been 
developed  at  various  periods  of  the  earth's  history.  It  is  not  the  pur- 
pose here  to  seek  the  ultimate  origin  of  these  lateral  stresses,  but  simply 
to  suggest  the  possibility  of  their  presence  as  a  cause  for  the  deformation 
of  the  region  under  consideration.  And  it  is  thought  that  most  of  the 
folds  and  faults  are  due  to  widespread  lateral  stresses,  which  have  been 
directed  in  such  a  way  as  to  cause  these  minor  movements. 

Summary  of  origin  of  folds  and  faults. — Of  the  various  causes  to 
which  the  formation  of  folds  and  faults  have  been  attributed,  a  number 
of  them  seem  to  have  no  application  to  the  deformation  of  rocks  in  the 
area  under  consideration;  namely:  igneous  activity,  expansion  due  to 
heat  from  adjacent  igneous  rocks,  increase  in  temperature  at  the  close 
of  the  glacial  period,  crystallization,  solution  of  underlying  formations, 
alteration  of  iron  sulphides,  weight  of  delta,  gas  pressure,  differential 
movement  of  beds  in  a  large  fault,  and  drag  of  icebergs.  Three  others — 
pressure  of  valley  walls,  release  of  pressure  by  erosion,  and  landslides — 
have  been  shown  wholly  inadequate  to  develop  stresses  sufficient  to 
deform  any  considerable  thickness  of  strata  in  place.  If  they  have  had 
any  effect,  it  has  been  by  the  addition  of  their  relatively  slight  force  to 
the  much  greater  stresses  already  in  the  rocks. 

Expansion  due  to  heat,  freezing  of  water,  and  hydration  of  minerals, 
may  have  helped  to  form  some  of  the  smaller  folds,  but  it  is  believed 

1  J.  Le  Conte,  Amer.  Jour.  Sci.-,  3d  Ser.,  XVIII  (1879),  4-Q- 

2  Salisbury  and  Atwood,  Jour.  Geol.,  V  (1897),  143. 
3 1.  C.  Russell,  op.  cit.,  p.  309. 


68  STUDIES  IN  MINOR  FOLDS 

that  these  agents,  in  the  main,  have  been  secondary,  increasing  dips 
started  by  other  forces  rather  than  initiating  them.  In  two  instances 
very  small  folds  involving  only  5  feet  or  less  of  strata,  are  thought  to  be 
due  to  the  pressure  of  glacial  ice,  which  because  of  their  topographic 
form  and  situation,  presented  very  abrupt  barriers  to  the  front  of  the 
ice.  All  of  the  larger  and  intermediate  folds,  and  many  of  the  smaller 
ones,  are  thought  to  be  due  to  widespread  tangential  stresses  in  the 
rocks,  the  origin  of  which  will  be  considered  later. 

AGE  OF  THE  FOLDS  AND  FAULTS 

The  age  of  the  folds  and  faults  will  be  considered  under  three  heads 
— pre-glacial,  glacial,  and  post-glacial.  An  attempt  also  will  be  made 
to  determine  still  more  explicitly  the  age  of  some  of  the  post-glacial 
deformations  by  their  relation  to  a  series  of  terraces. 

Pre-glacial. — A  number  of  the  larger  open  gentle  folds  are  considered 
pre-glacial,  the  low  fold  shown  in  Figure  1 2  being  one  of  the  smaller  ones 
belonging  to  this  group.  A  number  of  others  were  found,  but  no  good 
pictures  were  secured.  Still  more  marked  folds  of  this  age  and  type 
occur  farther  west  in  Ohio,  outside  this  area.  If  an  attempt  were  made 
to  fix  the  age  more  closely  we  can  say  they  are  post-Lower  Mississip- 
pian  and  pre-Pleistocene.  Both  Upper  Devonian  and  Lower  Missis- 
sippian  rocks  were  involved  in  the  deformations,  and  there  was  no  break 
in  the  sedimentation  between  the  Devonian  and  the  Mississippian  periods. 
Possibly  some  of  the  folds  were  formed  toward  the  close  of  the  Missis- 
sippian or  at  the  beginning  of  the  Pennsylvanian  period,  as  there  is  a 
general  unconformity  between  the  rocks  of  these  two  systems.  Or 
they  may  be  referable  to  the  Permian,  a  series  of  small,  gentle  folds 
being  formed  here  when  the  larger  and  more  intense  ones  were  developed 
in  the  Appalachians  to  the  southeast,  though  they  seem  rather  far 
removed  to  be  genetically  related  to  the  latter.  Or  there  is  a  possibil- 
ity they  may  have  been  formed  still  later,  between  the  Permian  and 
Pleistocene. 

Glacial. — As  has  been  noted  above  in  connection  with  the  origin  of 
folds,  a  few  small  ones  are  thought  to  be  due  to  the  pressure  of  glacial 
ice,  and  accordingly  are  of  Pleistocene  age.  They  are  considered  to 
belong  to  the  early  part  of  this  period,  being  formed  when  the  advancing 
ice  first  was  opposed  by  rather  abrupt  barriers.  Soon  after  the  first 
impact  of  the  front  of  the  glacier  with  the  barriers,  the  ice  doubtless 
was  deflected  above  them.  It  then  began  to  erode  the  crest  of  the 
escarpments  and  to  deposit  till  at  its  base,  thus  developing  an  easy 


STUDIES  IN  MINOR  FOLDS  69 

gradient  over  which  to  move.  The  folds  of  this  age  that  were  observed 
are  in  the  surface  coal  mine  (Fig.  35)  and  in  the  shales  near  Dunkirk 
(Fig.  36). 

It  is  possible  also  that  some  of  the  folds  and  faults,  though  not 
attributable  to  glacial  forces,  may  have  been  developed  during  the 
Pleistocene  period,  but  distinctive  evidence  marking  them  of  glacial 
age  is  wanting.  The  sharply  overturned  anticline  at  Thirty  Mile 
Point,  on  the  south  shore  of  Lake  Ontario,  has  been  called  glacial  in 
origin,  and  if  that  assumption  is  correct,  it  is  glacial  in  age.  If  so,  it 
was  formed  and  overturned  after  deposition  of  the  till  which  it  incloses 
beneath  the  overturned  crest. 

Post-glacial. — The  deformation  of  glaciated  surfaces  and  of  glacial 
deposits,  and  of  uneroded  tops  of  protruding  folds  and  faults,  is  recog- 
nized as  evidence  of  post-glacial  origin.  G.  K.  Gilbert  was  among  the 
first  to  recognize  the  post-glacial  age  of  folds  near  Caledonia  and  in 
Chautauqua  and  Jefferson  counties,  New  York.1  G.  F.  Mathews 
also  recognized  numerous  post-glacial  faults  in  the  slates  at  St.  John, 
New  Brunswick.2  The  faults  are  very  small,  having  a  displacement  of 
from  less  than  an  inch  to  5  inches,  but  the  glacial  surfaces  are  distinctly 
deformed  by  these  faults.  Much  more  recently  A.  C.  Lawson  described 
numerous  similar  post-glacial  faults  of  the  same  slight  magnitude, 
5  miles  west  of  Banning,  Ontario.3  J.  B.  Woodworth  has  studied  a 
series  of  small  post-glacial  faults  in  eastern  New  York,  and  has  com- 
pared them  with  faults  of  like  age  in  New  England,  Quebec,  and  New 
Brunswick.4  Of  the  faults  that  occur  in  the  five  areas  described  in 
eastern  New  York,  all  are  thrust  faults  in  highly  folded  strata  extending 
from  Lower  Cambrian  to  Lower  Silurian.  He  has  tabulated  the  move- 
ments in  several  of  the  series  of  small  faults,  and  has  taken  the  average 
displacement  per  yard  for  two  adjacent  areas,  and  gets  as  the  result 
i .  9  inches  in  a  yard,  or  336 . 7  feet  per  mile.5  No  such  minutely  deformed 
glaciated  surfaces  were  found  in  the  area  studied.  Possibly  this  is 
because  of  the  difference  in  the  general  attitude  of  the  rocks.  In  the 
Lake  Erie  region  they  are  in  general  flat-lying,  while  in  eastern  New 
York  they  are  highly  folded. 

1  G.  K.  Gilbert,  Amer.  Geologist,  VIII  (1891),  320-31;   and  Proc.  Amer.  Assoc. 
Adv.  Sci.,  XXXV  (1887),  227. 

2  G.  F.  Mathews,  Amer.  Jour.  Sci.,  3d  Ser.,  XL VIII  (1849),  5OI-3- 

3  A.  C.  Lawson,  Bull.  Seis.  Soc.  Amer.,  I  (1911),  159-66. 

4  J.  B.  Woodworth,  N.Y.  State  Mus.  Bull.  107,  Geol.  12  (1907),  pp.  5-28. 
s  J.  B.  Woodworth,  ibid.,  p.  19. 


70  STUDIES  IN  MINOR  FOLDS 

Faults  and  folds  with  uneroded  tops  are  in  reality  a  phase  of  defor- 
mation of  glaciated  surfaces,  because  the  loose,  easily  eroded  tops  rise 
above  the  general  level  of  the  glaciated  surface  and  deform  the  basal 
part  of  the  super jacent  glacial  deposits.  The  crest  of  a  fold  pro- 
truding up  into  the  glacial  till  and  including  till  beneath  its  overturned 
top,  occurs  along  the  southern  shore  of  Lake  Ontario,  at  Thirty  Mile  Point. 
Illustrations  of  this  fold  have  been  made  by  G.  K.  Gilbert,1  and  E.  M. 
Kindle  and  F.  B.  Taylor.2  This  fold  has  a  sharp  crest  of  much  shattered 
sandstones  and  shales  extending  up  into  the  glacial  clays  in  a  way  which 
indicates  that  the  fold  was  formed  after  the  drift  had  been  deposited 
and  the  ice  had  receded.  Similarly  sharp  crested  small  anticlines, 
though  not  overturned,  have  been  illustrated  by  F.  R.  Van  Horn.3 
These  folds  in  the  Chagrin  shales  have  their  sharp  crests  protruding 
into  the  superficial  glacial  till  in  a  manner  to  mark  them  clearly  as  post- 
glacial. Had  they  been  pre-glacial,  the  tops  of  soft,  broken  shale 
would  have  been  eroded.  A  fold  of  this  type  with  the  top  protruding 
into  the  drift  above  it  occurs  along  the  lake  shore  3  miles  east  of  Erie 
(Fig.  27). 

By  their  relation  to  terraces  and  terrace  deposits,  the  age  of  folds 
and  faults  can  be  determined  still  more  definitely,  so  we  can  say  they 
are  not  only  post-glacial  but  post- terrace  in  age.  Evidently  if  a  fold 
or  fault  deforms  the  terrace,  or  if  the  loose  shales  at  the  top  are  uneroded 
in  the  terrace,  they  are  younger  than  the  terrace.  E.  M.  Kindle  and 
F.  B.  Taylor  have  recognized  small  folds  in  the  Queenston  shale  south 
of  Lake  Ontario,  that  deform  low  terraces  and  so  are  known  to  be  more 
recent  than  those  terraces.4  In  the  region  south  of  Lake  Erie,  terraces 
are  deformed  by  folds  in  this  same  manner.  The  anticline  shown  in 
Figure  38  deforms  a  43 -foot  terrace.  The  gentle  limb  at  the  left  is 
200  feet  wide  and  the  steep  one  at  the  right  12  feet  wide.  Above  the 
crest  of  the  anticline  a  distinct  ridge  extends  across  the  surface  of  the 
terrace  in  the  direction  of  the  axis.  A  view  of  this  ridge  above  the  fold 
is  shown  in  Figure  37.  Other  folds,  above  which  distinct  low  ridges 
occur  in  the  terrace,  in  line  with  the  axis  of  the  fold,  are  shown  in  Fig- 
ure 18,  where  the  terrace  is  14  feet  high,  and  in  Figure  26,  where  the 
terrace  is  about  the  same  height. 

1  G.  K.  Gilbert,  Bull  Geol.  Soc.  Amer.,  X  (1898),  133,  Fig.  2. 

2  E.  M.  Kindle  and  F.  B.  Taylor,  Niagara  Folio,  No.  190  (1913),  Plate  19. 

3F.  R.  Van  Horn,  Bull.  Geol.  Soc.  Amer.,  XXI  (1009),  771-73,  Figs,  i,  2,  and 
Plate  54. 

4  E.  M.  Kindle  and  F.  B.  Taylor,  op.  cit.,  p.  15. 


STUDIES  IN  MINOR  FOLDS  71 

A  large  number  of  folds  were  found  with  their  uneroded  crests 
extending  up  definitely  into  the  terrace  material  above.  Protrusion 
by  a  fold  in  which  the  topmost  beds  are  resistant,  might  be  expected, 


FIG.  37. — A  low  ridge  deforming  the  terrace  above  the  fold  in  Figure  38 


FIG.  38. — An  unsymmetrical  fold  deforming  a  43-foot  terrace,  the  top  of  which 
is  shown  in  Figure  37.     Along  Elk  Creek  i  mile  southeast  of  Girard,  Pa. 

if  the  folds  are  older  than  the  terrace;  but  when  the  top  of  the  fold  con- 
sists of  thin-bedded  shales  and  sandstones,  the  uneroded  crest  gives 
evidence  that  the  fold  has  been  developed  since  the  formation  of  the 


72 


STUDIES  IN  MINOR  FOLDS 


terrace,  or  since  the  stream  abandoned  the  old  higher  channel.     Two 
illustrations  of  anticlines  from  which  streams  have  eroded  the  crests 


FIG.  39. — Anticline  in  the  Trenton  limestone  related  to  the  great  thrust  fault  at 
Prospect,  N.Y.  Having  eroded  the  crest  from  the  fold,  West  Canada  Creek  has 
shifted  its  channel  to  the  right. 


FIG.  40. — A  fold  from  which  the  crest  has  been  eroded  and  flood-plain  material 
deposited  on  the  eroded  top.     Along  the  Ashtabula  River,  near  Kingsville,  Ohio. 


are  shown  in  Figures  39  and  40.     The  former  is  a  fold  in  the  Trenton 
limestone  at  the  edge  of  the  large  fault  at  Prospect,  New  York.     Here, 


STUDIES  IN  MINOR  FOLDS 


73 


West  Canada  Creek,  having  eroded  the  crest  of  the  fold,  has  cut  its 
channel  more  deeply  to  the  right,  and  has  shifted  in  that  direction. 


FIG.  41. — Fold  with  crest  uneroded  in  a  20-foot  terrace.  The  book  above  the 
center  of  the  picture  covers  the  crest,  and  the  terrace  deposits  extend  down  into  the 
shale  between  the  two  books.  Near  North  East,  Pa. 


*boo*>- •'"••••     .*        v^i^^^^'^^^^^^ 


m 


FIG.  42. — Small  anticline  with  crest  uneroded  in  a  low  terrace.  Open  notebook 
behind  the  roots,  and  camera  case  near  end  of  small  thrust,  mark  top  of  shale.  Seven 
miles  southeast  of  Painesville,  Ohio. 

Another  anticline  with  eroded  crest  is  shown  in  Figure  40.     Since  the 
erosion  of  the  crest  the  stream  has  shifted,  and  the  materials  of  the 


74  STUDIES  IN  MINOR  FOLDS 

flood  plain  have  been  deposited  on  the  truncated  edges  of  the  strata, 
indicating  that  the  anticline  is  older  than  the  flood  plain. 

While  a  large  number  of  folds  having  their  crests  uneroded  occur,  it 
seemed  difficult  to  get  pictures  clearly  illustrating  this  condition.  The 
loose  shales  at  the  top  of  the  folds  frequently  are  very  like  the  fine 
material  above,  so  the  contrast  is  not  sufficiently  marked  to  show  well 
in  a  picture.  Figures  41  and  42  show  two  folds  from  which  the  loose 
shales  at  the  crest  have  not  been  eroded,  thus  marking  them  younger 
than  the  terraces  in  which  they  occur.  Figure  41  shows  the  detail  of 
the  crest  represented  in  Figure  8.  It  occurs  along  Sixteen  Mile  Creek, 
one-half  mile  south  of  North  East,  Pennsylvania,  in  a  terrace  20  feet 
high.  The  anticline  has  been  overturned  upstream,  and  the  crest 
(covered  by  the  upper  book)  has  been  forced  up  into  the  midst  of  the 
coarse  terrace  material.  The  lower  edge  of  the  book  at  the  right  rests 
on  the  topmost  part  of  the  shale  to  the  right  of  the  anticline.  The 
crest  of  this  fold,  overturned  upstream,  clearly  is  post-terrace.  Fig- 
ure 42  shows  another  small  anticline,  from  the  crest  of  which  the  loose 
shale  has  not  been  eroded.  The  open  notebook  (back  of  the  roots  to  the 
left  of  the  crest),  marks  the  juncture  of  shale  with  flood-plain  material, 
while  the  camera  case  marks  it  down  on  the  right  limb  of  the  fold.  A 
small  fault  with  a  horizontal  displacement  of  2  feet  and  3  inches  occurs 
at  the  right.  Figures  18,  26,  and  38  also  represent  folds  in  terraces  with 
their  crests  uneroded.  As  indicated  above,  the  age  of  these  folds  is  fixed 
clearly  as  younger  than  the  terraces  in  which  they  occur,  in  each  case 
where  the  non-resistant  crest  is  uneroded. 

In  the  same  manner  that  the  uneroded  top  of  a  fold  indicates  that 
it  is  more  recent  than  the  terrace  on  which  it  occurs,  so  the  uneroded 
top  of  a  fault  indicates  its  recency.  Two  faults  illustrating  the  differ- 
ence between  a  pre-terrace  fault  and  a  post-terrace  one  are  shown  in 
Figures  43  and  44.  Both  are  in  the  upper  part  of  the  Chagrin  shales 
along  Euclid  Creek,  about  9  miles  east  of  Cleveland.  Both  are  over- 
thrust  upstream  in  a  general  southeasterly  direction.  The  one  in 
Figure  43  is  in  a  terrace  10  feet  high,  2\  miles  south  of  Euclid,  and  the 
other  is  three-fourths  of  a  mile  farther  upstream,  in  a  terrace  8  feet 
high.  In  Figure  43  the  thin  sandstone  bed  above  (a)  on  the  downthrow 
side  of  the  plane  is  the  same  as  the  one  above  (a")  on  the  upthrow  side. 
The  overthrust  of  the  bed  from  the  right  of  (a)  would  carry  it  to  some 
such  point  as  (a'),  but  the  vertical  extension  of  the  overthrust  has  been 
eroded  to  the  gradient  plane  of  the  former  stream  channel  upon  which 
the  upper  material  of  the  terrace  has  been  deposited.  Thus  the  eroded 


STUDIES  IN  MINOR  FOLDS 


75 


top  indicates  clearly  that  the  displacement  occurred  before  the  forma- 
tion of  the  terrace.  In  contrast  with  this  condition,  the  fault  shown  in 
Figure  44  has  the  upthrow  side  still  uneroded  in  a  terrace  8  feet  in  height. 


FIG.  43. — A  small  fault  with  eroded  top  in  the  Chagrin  shales  near  Euclid,  Ohio. 
The  same  bed  occurs  above  (a)  and  (a"). 


FIG.  44. — Overthrust  fault  with  top  uneroded,  south  of  Euclid,  Ohio 

The  fault  plane  dips  at  a  very  low  angle  in  this  upper  part.  At  the 
left,  to  the  northwest,  it  dips  more  abruptly  beneath  the  floor  of  the 
valley.  The  horizontal  displacement  is  5  feet,  extending  from  (a)  to 


76  STUDIES  IN  MINOR  FOLDS 

the  camera  case  above  at  the  right.  The  end  of  the  upthrown  side 
abuts  against  the  flood-plain  material  at  the  right,  and  the  soft  shales 
have  not  been  eroded  from  the  top.  This  uneroded  top  proves  that 
the  displacement  is  younger  than  the  terrace. 

NATURE   AND   ORIGIN    OF   STRESSES   IN   ROCKS   IN   AREA 

Where  and  how  have  the  stresses  originated  that  formed  the  folds 
and  faults  ?  Are  they  merely  local,  or  are  they  general  for  the  region  ? 
Are  they  cumulative,  or  residual?  As  the  magnitude  of  the  deforma- 
tions may  have  direct  bearing  upon  these  questions,  that  will  be  noted 
first.  A  few  of  the  folds  have  a  width  of  from  300  to  500  feet,  but 
most  of  them  are  less  than  100  feet.  In  regard  to  the  thickness  of  the 
strata  involved,  some  folds  deform  terraces  40  to  60  feet  high,  and 
extend  an  unknown  distance  below  the  bottom  of  the  valleys.  The  size 
of  the  folds  would  seem  to  indicate  that  any  single  fold  does  not  reach 
a  very  great  depth.  In  some  instances  faults  below  grade  into  folds 
above,  and  these  faults  may  reach  down  for  a  considerable  distance. 
In  the  case  of  one  fold  along  Elk  Creek,  south  of  Girard,  Pennsylvania 
(Fig.  38),  there  is  a  constant  escape  of  gas  from  the  crest  where  the 
stream  crosses  it.  The  gas  horizons  of  this  region  lie  chiefly  between 
500  and  700  feet  in  depth.  This  seems  to  indicate  that  not  alone  the 
most  superficial  strata  are  affected  by  the  deformation.  A  number  of 
folds  of  the  same  magnitude  occur  in  the  area. 

Cumulative  stresses. — That  the  earth's  crust  has  a  very  considerable 
rigidity  which  must  be  overcome  before  deformation  can  take  place  is  a 
fact  now  generally  recognized.  That  the  great  movements  of  the  earth's 
crust  are  periodic  has  been  emphasized  by  many  eminent  geologists.1 
This  periodicity  has  been  proved  by  the  earth's  history.  R.  T.  Cham- 
berlin  recently  has  summarized  the  diastrophic  periods  of  the  Paleozoic, 
noting  their  relative  importance  and  value  as  criteria  for  separating  the 
rock  systems.2  Between  the  periods  of  great  deformation,  inter-periods 
of  relative  quiescence  have  occurred,  during  which  land  masses  remained 
in  a  stable  condition,  while  erosion  has  proceeded  sufficiently  long  to 
reduce  areas  to  the  base-leveled  condition  of  a  peneplain.  Because  of 
the  rigidity  of  the  earth,  and  of  this  periodicity  of  the  great  diastrophic 
movements,  it  is  conceivable  that  there  are  long  periods  of  stress  accumu- 

XT.  C.  Chamberlin  and  R.  D.  Salisbury,  Geology,  I  (1905),  588-89,  and  III, 
192-93;  T.  C.  Chamberlin,  Jour.  Gcol.,  XVII  (1909),  689;  C.  Schuchert,  Bull  Geol. 
Soc.  Amer.,  XX  (1908),  500;  Bailey  Willis,  Science,  XXXI  (1910),  246-48. 

2  R.  T.  Chamberlin,  Jour.  Geol.,  XXII  (1914),  315-45. 


STUDIES  IN  MINOR  FOLDS  77 

lation,  in  which  the  stresses  become  more  and  more  acute  until  they  are 
sufficiently  strong  to  overcome  the  strength  of  the  earth's  crust  and  its 
rigid  interior.  When  this  mastering  degree  of  intensity  has  been  reached, 
readjustment  by  movement  takes  place  in  the  various  types  of  deforma- 
tion. These  adjustments  continue  until  all  the  stresses  are  more  or  less 
perfectly  compensated.  After  each  great  deformative  period  there 
follows  a  period  of  quietude  in  which  the  accumulation  of  stresses  again 
begins  to  develop  toward  a  higher  and  higher  intensity. 

If  there  are  these  long  intervals  of  stress  accumulation  preceding 
each  diastrophic  movement,  it  is  possible  that  although  incompetent 
to  deform  the. great  masses  of  the  earth's  exterior,  they  still  may  have 
sufficient  force  to  overcome  locally  some  of  the  weaker  parts,  particu- 
larly if  in  addition  to  the  more  general  stresses  the  rocks  of  an  area  are 
subjected  to  additional  local  ones.  That  these  cumulative  stresses  are 
likely  to  be  widespread  may  be  deduced  from  the  large  areas  affected 
by  compensating  adjustments. 

It  is  conceived  then  that  during  a  period  of  relative  quietude  for 
this  area,  stresses  have  accumulated  which,  possibly  by  the  addition  of 
local  stresses,  to  be  noted  later,  have  reached  an  intensity  sufficient  to 
deform  the  rocks  on  a  small  scale.  If  the  great  periodic  or  inter-periodic 
stresses  have  been  accumulating  in  this  area,  and  have  contributed,  in 
part  at  least,  to  the  deformation  of  the  rocks,  the  small  folds  and  thrust 
faults  indicate  that  they  are  largely  lateral,  or  tangential. 

Residual  stresses. — In  connection  with  the  climactic  accumulation  of 
stresses  with  the  consequent  strains  and  deformative  movements,  it  was 
noted  that  the  compensation  of  the  force  developed  might  be  more  or 
less  complete.  If  the  compensation  were  absolutely  complete,  the  new 
era  following  the  deformative  one  would  start  out  with  a  clean  record. 
Thus  one  series  in  a  cycle  would  be:  stresses  developed  slowly  to  great 
intensity,  great  diastrophic  movements,  stresses  all  relieved,  and  rocks 
perfectly  at  ease  until  the  beginning  of  a  new  series  of  cumulative  stresses 
is  initiated.  Another  conception  may  be  that  compensation  is  not  com- 
plete; that  after  all  the  force  of  the  great  stresses  competent  to  cause 
deformation  has  been  relieved,  there  still  remain  residual  stresses, 
which,  though  real  in  character,  are  incompetent  to  carry  the  deforma- 
tion farther.  Thus  the  new  era  succeeding  the  deformation  period 
would  have  bequeathed  to  it  some  of  the  stresses  which  may  have  been 
initiated  early  in  the  preceding  period  of  general  quietude. 

Still  another  conception  may  be  that  compensation  is  variable 
throughout  any  large  area  affected  by  deformative  forces,  not  alone 


78  STUDIES  IN  MINOR  FOLDS 

because  of  the  variable  rigidity  and  elasticity  of  the  rocks,  but  more 
largely  in  the  localization  of  the  forces  engendered  by  the  stresses,  and 
the  alignment  of  those  forces  in  one  general  direction.  Illustrations  of 
this  localization  and  alignment  are  seen  in  the  closely  folding,  over- 
turning, and  thrust  faulting  of  the  central  and  southern  parts  of  the 
Appalachians.  If  it  be  true  that  a  great  -thrust  of  part  of  the  earth's 
exterior,  and  possibly  a  part  of  the  interior,  was  directed  against  the 
southeastern  margin  of  the  Appalachian  region,  it  is  possible  that  compen- 
sation was  most  perfect  along  this  margin,  where  the  force  was  applied 
and  where  the  close  folds  were  overturned,  broken,  and  overthrust 
one  far  upon  another.  Toward  the  northwest,  compensation  may  have 
been  less  complete  as  the  folds  became  more  open.  Still  farther  to  the 
northwest,  beyond  where  the  gentle,  open  folds  were  formed,  lateral 
stresses  may  have  developed  which,  though  considerable  in  intensity, 
were  incompetent  to  deform  the  rocks.  It  is  the  conception,  then,  for 
the  area  studied,  that  tangential  stresses  very  considerable  in  amount 
were  initiated  here  at  the  time  when  the  marked  diastrophic  movements 
formed  the  great  Appalachian  structural  unit,  and  that  these  stresses 
have  remained  as  a  residuum  since  that  time.  It  is  thought  that  to 
these  residual  stresses  later  stresses  were  added,  making  their  combined 
force  sufficient  to  fold  and  rupture  the  rocks.  J.  Barrell,  in  his  recent 
studies,  has  expressed  the  idea  that  strains  within  the  earth's  crust 
may  be  borne  for  very  long  periods  of  time.1 

RELATION   TO   LARGER   MOVEMENTS 

Having  noted  that  very  considerable  residual  stresses  probably 
have  existed  for  an  extremely  long  time,  it  is  the  purpose  now  to  link 
the  minor  movements  of  this  area  with  much  larger  ones;  the  up  tilt- 
ing of  the  northern  part  of  the  Great  Lakes  area  and  the  region  to 
the  northeast,  and  the  uplift  and  deformation  of  the  Harrisburg  pene- 
plain in  northern  Pennsylvania,  northeastern  Ohio,  and  southern  New 
York. 

Northeastward  tilting. — It  has  long  been  recognized  that  the  region 
of  the  Great  Lakes  and  the  area  to.  the  northeast  of  these  lakes  have 
been  undergoing  a  tilting  movement  during  and  since  the  Pleistocene. 
In  this  movement  the'  rise  has  increased  in  magnitude  from  the  Great 
Lakes  region  toward  the  northeast.  From  a  large  number  of  measure- 
ments of  changes  in  the  levels  of  the  lakes  on  the  north  and  south  sides, 

1  J.  Barrel),  Jour.  GeoL,  XXII  (1914),  310. 

2  G.  K.  Gilbert,  Eighteenth  Ann.  Kept.  U.S.G.S.,  XVIII  (2)  (1896-97),  636. 


STUDIES  IN  MINOR  FOLDS  79 

G.  K.  Gilbert1  has  deduced  the  result  of  a  tilting  .42  of  a  foot  for  100  miles 
in  one  hundred  years.  The  tilting  during  and  since  the  Pleistocene  also 
has  been  measured  and  computed,  by  determining  the  amount  of  warp- 
ing of  the  old  water  lines  marked  by  beach  ridges  and  cut  bluffs  which 
are  now  far  above  the  present  level  of  the  lakes.  A  large  number  have 
worked  on  the  problems  of  the  uplift  and  tilting  of  this  lake  area,  and 
H.  L.  Fairchild  in  a  recent  article  has  given  the  bibliography  of  this 
work.2  The  direction  of  the  isobases  for  New  York  and  northern  Penn- 
sylvania, given  by  Fairchild  "with  an  inclination  from  the  latitude 
parallels  of  20°,  70°  divergence  from  the  meridians,"3  corresponds  closely 
with  the  extensions  of  those  given  by  J.  W.  Goldthwait  for  the  Lake 
Michigan -Huron  region;4  also  with  those  given  earlier  by  G.  K.  Gilbert 
for  the  entire  Great  Lakes  region.5  Just  where  the  hinge  for  this  uplift 
should  be  placed  with  reference  to  Lake  Erie  is  not  definitely  settled. 
Goldthwait  apparently  would  place  it  at  the  extreme  eastern  end  of  the 
lake,6  while  Fairchild  would  place  it  west  of  the  center. 

If  then,  the  hinge  line  of  this  uplift  passes  through,  or  along,  the  edge 
of  the  area  studied,  this  area  is  in  a  critical  position  with  reference  to 
the  uplift.  The  position  is  critical  because  of  tangential  stresses  which 
may  have  been  related  to  the  tilting  in  a  zone  parallel  to  the  hinge. 
That  the  tilting  and  tangential  movements  have  been  synchronous  is 
suggestive.  The  tilting  begun  during  the  Pleistocene  continues  to  the 
present.  Numerous  folds  and  faults  are  post-glacial,  some  giving  evi- 
dence of  reaching  almost  to  the  present  time. 

If  tangential  stresses  are  related  to  this  uplift,  folds  resulting  from 
them  should  have  their  axes  trending  in  a  general  way  parallel  with  the 
hinge  line  and  the  isobases.  As  noted  above,  the  isobases  trend  about 
80°  west  of  north,  when  extended  as  straight  lines  from  the  Lake 
Michigan-Huron  region,  but  if  the  isobases  curve  southward  across 
Lake  Erie,  the  direction  would  be  north  60°  or  70°  west. 

Table  V  gives  the  direction  of  the  axes  for  folds  in  the  Lake  Erie 
region,  of  which  illustrations  are  shown,  and  is  quite  representative. 
While  a  very  few  have  axes  either  about  east  and  west  or  north  and  south, 
two-thirds  have  a  northwest  trend,  the  majority  lying  between  N.40°W. 

'G.  K.  Gilbert,  Eighteenth  Ann.  Kept.  U.S.G.S.,  XVIII  (2)  (1896-97),  636. 

2  H.  L.  Fairchild,  Bull.  Geol.  Soc.  Amer.,  XXVII  (1916),  255-62. 

3  H.  L.  Fairchild,  ibid.,  238,  Plates  10  and  12. 

4J.W.  Goldthwait,  Canada  Dept.  Min.  Geol.  Surv.  Mem.  10  (1910),  Fig.  3,  opp.  p.  40. 

5  G.  K.  Gilbert,  op.  cit.,  p.  640,  Fig.  100. 

6  J.  W.  Goldthwait,  Bull.  Geol.  Soc.  Amer.,  XXI  (1910),  Plate  5,  opp.  p.  233. 


8o  STUDIES  IN  MINOR  FOLDS 

and  N.8o°W.,  and  about  one- third  have  a  northeast  trend.  The  trend 
of  the  folds  may  seem  too  variable  to  align  them  into  one  or  even  two 
series,  but  minor  folds  of  any  series  are  not  necessarily  closely  parallel 
with  one  another.  For  comparison,  the  trend  of  a  number  of  folds  on 
the  northwest  border  of  the  Appalachians  was  determined  from  the 
geological  folios  and  arranged  in  Table  VI.  This  table  shows  a  large 
variation  in  the  trend  of  the  axes  of  the  smaller  folds  of  a  series  adjacent 
to  the  larger  Appalachian  structures.  A  comparison  of  Tables  V  and 

TABLE  V 

SHOWING   DIRECTION   OF   AXES    OF   FOLDS   IN   THE   LAKE   ERIE    REGION 


Fig. 

Fig. 
Fig. 
Fig. 
Fig. 
Fig. 

2. 
27. 
28. 
12. 
40. 

4- 

Northwest  Trend 

N.io°W.        Fig.  14.    N.5o°W. 
N.2o°W.        Fig.  31.    N.6o°W. 
N.3o°W.        Fig.  33.    N.6o°W. 
N.3s°W.        Fig.  25.    N.8o°W. 
N.4o°W.        Fig.  34.    N.8o°W. 
N.45°W.        Fig.  42.     N.8o°W. 

East  -West  and  North-South  Trend 

Fig.  23.    E.-W. 
Fig.  38.    N.-S. 

Northeast  Trend 

Fig.  ii.     N.io°E. 
Fig.  26.    N.25°E. 
Fig.    8.    N.35°E. 
Fig.  41.     N.35°E. 
Fig.  24.    N.5o°E. 

TABLE  VI 

SHOWING  TREND  OF  AXES   OF   FOLDS  ALONG  THE  NORTHWESTERN  EDGE  OF  THE 
APPALACHIANS  IN  PENNSYLVANIA 

N.is°E.  N.35°E.  N.8o°E. 

N.i5°E.  N.4o°E.  N.8o°E. 

N.28°E.  N.45°E. 

N.30°E.  N.6o°E.  N.42°W. 

N.35°E.  N.7o°E.  N.8o°W. 

VI  shows  about  the  same  degree  of  variation  in  both,  even  though  the 
directions  in  the  latter  represent  the  axes  of  folds  along  the  border  of 
the  Appalachians. 

Doming  of  peneplain. — M.  R.  Campbell1  has  adduced  evidence  on  a 
physiographic  basis  to  show  that  the  Harrisburg  peneplain  has  been 
deformed  by  an  irregular  domelike  uplift,  with  the  maximum  of  eleva- 
tion in  McKean  and  Potter  counties,  Pennsylvania,  and  in  southern 
New  York.  This  peneplain  rises  from  500  feet  near  Harrisburg,  to 
2,200  feet  in  the  northern  part  of  the  state.  The  area  along  the  southern 
border  of  Lake  Erie  forms  the  northwestern  part  of  this  domelike  uplift, 

'M.  R.  Campbell,  Bull.  Geol.  Soc.  Amer.,  XIV  (1902),  277-96. 


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STUDIES  IN  MINOR  FOLDS  81 

and  in  this  part  of  the  dome  isobases  trend  north  60°  to  70°  east.  While 
the  axes  of  the  majority  of  folds  trend  northwest,  a  second  series  have 
axes  trending  in  a  northeasterly  direction,  and  these  are  closely  parallel 
with  the  direction  of  the  isobases  on  the  northwest  side  of  the  dome. 
It  is  worthy  of  note  that  the  trace  of  the  faults  in  the  Syracuse  region 
is  nearly  east  and  west,  as  they  lie  on  the  north  side  of  the  dome,  and 
parallel  the  general  trend  of  the  isobases  there.  Thus,  of  the  two  series 
of  folds,  one  series  with  northwest  trend  parallels  the  isobases  of  tilting 
to  the  northeast,  while  the  other  parallels  the  isobases  of  the  domed 
peneplain.  (See  Plate  III.) 

This  peneplain  is  of  early  Tertiary  age,  so  its  deformation  has  been 
since  that  time.  How  recent  elevation  has  been  is  not  known.  It  is 
quite  possible  it  may  have  been  very  recent,  or  it  may  have  continued 
to  the  present.  If  elevation  in  the  doming  has  been  recent,  we  have 
elevation  of  two  types  at  the  same  time  in  adjacent  regions. 

While  in  the  elevation  of  these  two  areas,  the  vertical  component  in 
the  stresses  was  doubtless  dominant,  it  is  thought  there  would  be  a 
horizontal  component  also,  which  would  increase  in  intensity  toward 
the  margin  of  the  dome  and  toward  the  hinge  of  the  tilted  area.  Were 
the  uplifts  synchronous,  lateral  stresses  from  the  south  and  southeast 
would  meet  those  from  the  northeast  at  an  angle,  and  the  two  sets  be 
combined.  If  uplifts  alternated  in  time,  stresses  first  from  one  direction 
and  then  from  the  other  would  be  dominant.  The  area  studied  is  then 
in  a  most  critical  position,  being  in  the  border  zone  of  these  two  large 
movements,  caught  as  a  wedge  between  the  two  uplifts.  It  is  at  least 
very  significant  that  in  the  open  part  at  the  western  end  of  the  area 
where  the  isobases  diverge,  the  folds  are  scattered,  and  the  tangential 
movement  is  comparatively  slight,  while  in  southern  New  York,  on  the 
north  side  of  the  dome,  where  the  isobases  converge  and  the  uplifts 
come  together  and  possibly  overlap,  the  folds  are  larger,  and  over  thrusts 
of  greater  magnitude  occur.  Thus  it  is  thought  that  in  connection 
with  these  two  great  movements  of  tilting  and  doming,  lateral  stresses 
have  been  initiated  in  this  border  area,  competent  to  cause  the  minor 
tangential  movements. 

SUMMARY 

The  following  conclusions  have  been  reached  with  reference  to  these 
minor  deformations  in  the  area  bordering  on  and  adjacent  to  the  south- 
ern edge  of  Lake  Erie.  The  deformation  consists  of  folds  and  thrust 
faults,  indicating  the  predominance  of  lateral  stresses;  the  minor  folds 
present  most  of  the  types  common  in  major  ones,  though  typical  closed 


82  STUDIES  IN  MINOR  FOLDS 

and  recumbent  folds  are  absent;  of  the  many  explanations  considered 
for  the  origin  of  the  folds  and  faults,  most  of  them  have  been  rejected 
as  wholly  inapplicable  or  markedly  incompetent  quantitatively  for  this 
area;  while  ice  expansion  and  weathering  may  have  caused  some  very 
small  superficial  flexures,  and  a  few  very  small  folds  in  weak  or  disturbed 
strata  may  be  due  to  glaciation  and  landslides,  it  is  thought  that  most 
of  the  folds  and  faults  are  the  result  of  widespread  lateral  compressive 
stresses;  a  few  of  the  folds  are  pre-Pleistocene,  possibly  Permian  or 
later,  a  few  very  small  ones  are  Pleistocene,  but  most  of  them  are  post- 
glacial, and  a  number  are  post- terrace;  cumulative  stresses  developing 
between  the  great  diastrophic  periods  are  thought  to  have  affected  the 
rocks  of  this  area,  and  possibly,  also,  some  strains  residual  from  one  or 
more  of  the  great  deformative  periods  have  been  bequeathed  to  the 
rocks  here,  and  these  strains  were  linked  with  later  ones  initiated  by 
recent  movements;  and  finally,  the  minor  movements  of  the  area  are 
thought  to  be  genetically  related  to  the  two  larger  ones — tilting  of  the 
Great  Lakes  region  to  the  northeast,  and  doming  of  the  Harrisburg 
Peneplain  to  the  southeast. 


INDEX 


INDEX 


Age  of  folds  and  faults,  68 

Alaska,  17 

Alignment  of  forces,  78 

Allegheny  Plateaus,  23 

Alteration  of  iron  sulphide,  50 

Andover,  4;  quadrangle,  14 

Anticline,  4;  closed,  9;  open,  9,  10; 
overturned,  7,  8;  recumbent,  9;  sym- 
metrical, 4;  unsymmetrical,  5 

Anticlinoria,  14 

Aplite,  17 

Appalachian  Mountains,  67 

Arbuckle,  anticline,  20;  limestone,  18, 19, 
20;  Mountains,  3,  14,  17,  25,  36,  67 

Ashtabula,  County,  30;   River,  24,  34 

Australia,  3 

Bain,  H.  F.,  58 

Ball,  S.  H.,  and  Smith,  A.  F.,  54 

Banning,  Ontario,  69 

Baraboo,  Wis.,  67 

Barrell,  J.,  78 

Basalt,  17 

Bascom,  F.,  16 

Beaver  quadrangle,  36 

Becker,  G.  F.,  60 

Becraft  limestone,  25 

Bedford,  formation,  6;  shale,  27,  31 

Beekmantown  limestone,  25 

Berea  grit,  27,  31 

Big  Horn  and  Yellowstone  rivers,  57 

Big  Horn  Mountains,  58 

Black  Hills,  12,  13 

Black  River  Canal  Feeder,  37 

Black  River  limestone,  25,  26 

Bois  d'Arc  limestone,  18 

Boonville,  N.Y.,  37 

Brooks,  F.  H.,  17 

Burlington,  Ontario,  7,  8,  27 

Caledonia,  N.Y.,  69 
Cambrian,  18,  19,  69 
Campbell,  M.  R.,  33,  80 


Canadaway  Creek,  24,  65 

Caney  shale,  18 

Carinate  fold,  14 

Cascade  Mountains,  48 

Cashaqua  shale,  28 

Cattaraugus,  Creek,  49;  formation,  27,  30 

Cedar  Valley  limestone,  37 

Chagrin,  Falls,  5;    formation,  27,  29,  47; 

River,  5,  24;  shales,  70,  74,  75 
Chamberlin  and  Salisbury,  7,  16,  43,  45, 

58,  66,  76 

Chamberlin,  R.  T.,  4,  76 
Chamberlin,  T.  C.,  4,  76 
Chautauqua,  County,  49,  69;   Creek,  24 
Chazy,  formation,  26;  limestone,  25 
Chemung,  brachiopods,    29;    formation, 

25>  27>  3°>  42;  sandstones,  14 
Cherokee  shales,  54 
Chimney  Hill  limestone,  18 
Cincinnati  Arch,  23 
Clarke,  J.  M.,  27,  28,  29,  41;  and  Luther, 

28;  and  Schuchert,  25 
Cleveland,  3;   Brick  and  Clay  Company, 

62;  shale,  27,  30 
Clinton  beds,  25 

Closed  anticline,  10,  27,  28,  29,  41,  82 
Clymer  quadrangle,  24 
Coeymans  limestone,  25 
Compensating  adjustments,  77,  78 
Cone-in-cone,  29 

Conneaut  Creek,  24,  34,  35;  Ohio,  4 
Conneautville,  Pa.,  65 
Connecticut  Valley,  15 
Cook  Point,  48 
Coon,  W.  E.,  4 
Corry  sandstone,  27,  31 
Crawford  County,  Pa.,  31 
Crosby,  W.  O.,  59 
Crusher,  Okla.,  9,  20 
Cumulative  stresses,  76 
Gushing,  H.  P.,  26 
Cussewago  beds,  25,  27,  31 
Cuyahoga  River,  24 


86 


STUDIES  IN  MINOR  FOLDS 


Daly,  R.  A.,  16 
Dana  Lake,  35 
Darton,  N.H.,  13 
Deep  well  at  Erie,  Pa.,  57 
Deformation,  by  landslides,  61;   by  solu- 
tion, 54;  of  terrace,  70 
Des  Plaines  River,  52 
Devonian,  18,  25,  27,  28,  29,  30,  68 
Devono-Carboniferous,  31 
Dewitt,  N.Y.,  48 
Diabase,  17 

Differential  movements,  63 
Disconformity,  26 

Displacement  in  faults,  44-47,  56,  69 
Dome,  n,  19,  20 

Doming  of  peneplain,  33,  80,  81,  82 
Drainage  changes,  34 
Dunkirk,  N.Y.,  3,  49,  65 

East  Onondaga,  59 

Eighteen  Mile  Creek,  27 

Elk  Creek,  14,  24,  34,-  41,  45,  47,  58,  76 

Erie,  4,  41,  42 

Esopus  grit,  25 

Euclid,  Ohio,  and  Creek,  74 

Fairchild,  H.  L.,  35,  69 

Falls  Creek,  12,  19 

Faulting,  57 

Faults,  41,  43-48 

Ferrous  sulphate  soluble,  51 

Folds,  1-82;  carinate,  14;  due  to  com- 
pacting, 57;  gas  pressure,  63;  intra- 
formational,  36,  37;  isoclinal,  14; 
monoclinal,  14;  origin  of,  48-68; 
parallel,  37,  38;  transverse,  38,  39; 
types,  4-16,  19,  20 

Folios  with  folds  due  to  vulcanism,  48 

Franks  conglomerate,  18 

Freedom,  Pa.,  36 

Gabbro,  17 

Gaines,  folio,  30,  31,  32;    quadrangle,  30 

Galena  dolomite,  58 

Gardeau  shales,  28 

Gartz,  Frank,  4 

Gas,  escape,  63;  pressure  low,  63 

Gasconade  formation,  54 


General  relations  and  direction  of  axes, 

16 

General,  structure,  35;   types  of  folds,  36 
Genesee,  River,  28;  shale,  25 
Geneva,  Ohio,  23 
Geologic  history,  32 
Gilbert,  G.  K.,  4,  13,  14,  15,  49,  61,  64, 

69,  70,  78,  79 

Girard,  Pa.,  4,  7,  14,  43,  45 
Girard  shales,  27,  29,  41,  43,  44,  51 
Glacial,  age  of  folds,  68;   deposition,  34; 

erosion,  34 
Glaciation,  63,  82 
Glacio-Lacustrine  substage,  35 
Glenn,  L.  C.,  27,  30,  31 
Goldthwait,  J.  W.,  79 
Grand  River,  24,  34;   Glacial  Lobe,  34 
Granite,  17 
Gravity,  effects  of,  60 
Grimes  sandstone,  28 
Gulf  Coastal  Plain,  54 

Hall,  J.,  28,  29,  30,  50 

Hamilton  beds,  25 

Haragan  marl,  18 

Harrisburg  peneplain,  deformed,  78,  80, 

81,  82;  age  of,  33,  81 
Hatch  shale,  28 
Henry  Mountains,  1 2 
Henry  house  shale,  18 
Hice,  R.  R.,  36,  37 
Hinge  of  uplift,  79 
Homocline,  16 
Hopkins  Creek  Estuary,  60 
Hopkins,  T.  C.,  23,  50,  59,  61 
Huron,  River,  29;  shale,  27,  29,  51 

Ice  expansion  as  cause  of  folds,  49/82 

Igneous  activity  as  cause  of  folds,  1 7 

Intra-formational  folds,  36,  53 

Introduction,  i 

Isobases  of  tilted  area,  79 

Isoclinal  folds,  14 

Ithaca,  N.Y.,  48,  55 

Jamesville,  N.Y.,  59 
Jefferson  County,  N.Y.,  49,  69 
Joplin  folio,  54 


INDEX 


Kelley's  Island,  66 

Kennedy,  W.,  54 

Keweenawan  dolomite,  48 

Kindle,  E.  M.,  37;  and  Taylor,  F.  B.,  26, 

27,  64,  70 
Kingston  beds,  25 
Kingsville,  4 
Knapp  formation,  27 

Lake,  Erie,  3,  28,  35,  38,49,  69;  Lahon- 
tan,  61;  Mono,  37,  67;  Ontario,  3,  27, 
60,  64;  Plain,  23;  Zug,  61;  Zurich,  61 

Landslides,  61,  82 

Lateral  stresses,  62,  81,  82 

Lawson,  A.  C.,  69 

LeConte',  J.,  64,  67 

Leith,  C.  K.,  21 

Lesley,  J.  P.,  35 

Leverett,  F.,  34 

Limonite,  51 

Little  Elk  Creek,  43 

Little  Falls,  N.Y.,  55 

Local  structures,  36 

Localization  of  forces,  78 

Location  and  area,  22 

Lockport  limestone,  25 

Logan  County,  Ark.,  52 

Logan  River,  Utah,  60 

Lorraine  beds,  25 

Lower  Kittanning  clay,  36 

Lowville  limestone,  25,  26 

Luther,  D.  D.,  27,  29,  56 

Lyons  quarry,  Chicago,  52 

Magnetite,  51 

Manheim,  N.Y.,  48 

Manlius  limestone,  25 

Manlius,  N.Y.,  59 

Marcasite,  51 

Marcellus,  59;  shale,  25 

Maryland,  16 

Mathews,  E.  B.,  12,  16 

Mathews,  G.  F.,  69 

Maumee  Lake,  35 

McGee,  W.  G.,  37 

McKean  County,  Pa.,  80 

Meadville,  Pa.,  4,  34,  38,  39,  59,  61 

Medina  sandstone,  25 


Michigan,  3 

Middle  Kittanning  coal,  37 

Middlesex  black  shale,  28 

Miles  Grove,  42 

Mill  Creek,  Ohio,  62;  Pa.,  24 

Miller  County,  Mo.,  54 

Miller,  W.  J.,  26,  36,  54,  63 

Minor  folds,  3,  17 

Mississippian,  formations,  18,  25,  27,  31; 

period,  68 

Mono  Valley,  61,  64 
Monoclinal,  14,  15 
Montana,  57 

Nature  and  origin  of  stresses,  76 

New  Brunswick,  69 

New  England,  69 

New  Scotland  beds,  25 

New  York,  Chicago,  St.  Louis  R.R.,  4? 

New  York,  41,  55,  69,  80 

Niagara,  Gorge,  26;  folio,  60;  limestone, 

13,  52;  quadrangle,  27 
Nipogon  Basin,  Canada,  48 
North  East,  4,  8-14,  43,  74 
Northeastward  tilting,  78 
Nova  Scotia,  37 

Ohio,  3,  30 

Oklahoma,  3,  17 

Olcott,  N.Y.,  27 

Olean  conglomerate,  31 

Oheida  conglomerate,  25 

Onondaga,  County,  56;  limestone,  25 

Ontario,  37 

Open  anticline,  9,  n 

Orangeville  shale,  25,  27 

Ordovician,  18,  25,  26 

Origin  of  folds  and  faults,  48 

Oriskany  beds,  25 

Orton,  E.,  30 

Oswayo  formation,  27,  31 

Ouachita  Mountains,  67 

Outline,  i 

Overturned  anticline,  7 

Paine  Creek,  7,  46,  47 
Painesville,  4,  10 
Parallel  folds,  37 


88 


STUDIES  IN  MINOR  FOLDS 


Passage  shales,  28 
Pegmatite,  17 

Peneplain,  deformed,  80,  82;  Harrisburg, 
33,81;  Schooley,  33;  Worthington,  33 
Pennsylvania,  3,  35 
Pennsylvanian,  18,  25,  31 
Periodicity  of  crustal  movements,  76 
Permian,  18,  68,  82 
Physiographic  history,  33 
Piedmont,  12,  1 6 
Pirsson,  L.  V.,  59 
Pleistocene,  32;   age,  68,  82;   tilting,  78, 

79 

Porphyry,  17 

Portage,  beds,  25,  27;  group,  28 
Post-glacial,    age,     82;      changes,     35; 

deposits,  32 
Post- terrace,  82 
Potter  County,  80 
Powell,  J.  W.,  1 6 
Pre-glacial,  68 
Pre-Pleistocene,  82 
Presque  Isle,  32 
Pressure,  gas,  63;  ice,  49 
Prospect,  N.Y.,  26,  63,  72 
Prosser,  C.  H.,  6,  27,  29,  30,  31,  32,  57 
Provo  delta,  Utah,  60 
Purpose,  3 
Pyrite,  51 

Quartz-monzonite,  17 

Quaternary,  32,  37 

Quebec,  67 

Queenston,  26;  shale,  26,  27,  41,  60 

Radial  shortening,  57,  58 
Reagan  sandstone,  18 
Recumbent  fold,  8,  9,  82 
Reeds,  C.  A.,  14,  17,  19 
Relation  to  larger  movements,  78 
Remsen  quadrangle,  26 
Residual  stresses,  77 
Rhinestreet  black  shale,  28 
Riceville  shale,  25,  27,  31,  38 
Richmond  beds,  25,  26 
Rise  in  temperature  of  rocks,  49 
Rochester,  36;  shale,  25 
Rocky  Mountains,  48 


Rogers,  G.  S.,  57 
Rondout  waterlime,  25 
Russell,  I.  C.,  37,  61,  64,  67 

Salina,  25,  56 

Salisbury  and  Atvvood,  67 

Salisbury,  R.  D.,  4 

Sandusky,  3 

Sardeson,  F.  W.,  63,  64 

Schneider,  P.  F.,  41,  48,  55,  56 

Schooley  peneplain,  33 

Schuchert,  C.,  27,  76 

Schoharie  grit,  25 

Sedimentary  rocks,  18 

Seneca  Lake,  28 

Shaler,  N.  S.,  54 

Sharon  conglomerate,  25,  31 

Sharpsville  sandstone,  25 

Shenango  beds,  25 

Shortening  by  drop  of  hypothenuse,  56 

Siebenthal,  C.  E.,  54 

Sierra  Nevada  Mountains,  48 

Silurian,  1 8,  25,  69 

Simpson  formation,  9,  19,  20,  36 

Sixteen  Mile  Creek,  14,  24,  43,  44,  74 

Smallwood  and  Hopkins,  23,  50,  59,  61 

Solway  well,  56 

St.  Elizabeth  limestone,  54 

St.  John,  New  Brunswick,  69 

Stone,  R.  W.,  33 

Stony  Island,  13,  65 

Stresses  due  to  crystallization  of  lime- 
stone, 53 

Structure,  19;  general,  35;  local,  36 

Summary,  81;  of  minor  folds,  21;  of 
origin  of  folds,  67 

Sunbury  shale,  27 

Swanville,  45 

Sycamore  limestone,  18 

Syenite,  26 

Sylvan  shale,  18 

Symmetrical  anticline,  4,  5,  45 

Syncline,  13 

Synclinoria,  14 

Syracuse,  48,  56,  81 

Table  I,  18;  II,  25;  III,  27;  IV,  28; 
V,  80;  VI,  80 


INDEX 


89 


Taconic  Mountains,  67 

Terraces,  24;  deformed,  70,  71 

Thirty  Mile  Point,  64,  70 

Thompson's  Ledge,  25,  32 

Tilting  of  lake  region,  78,  82 

Topography  of  area,  23 

Transverse  folds,  38,  40 

Trend  of  axes,  39,  40,  80 

Trenton  Falls,  36,  53,  59,  63 

Trenton  limestone,  25,  26,  36 

Trumbull  County,  30 

Tully  limestone,  25 

Twenty  Mile  Creek,  24,  34,  37,  38,  47 

Types  of  folds,  4,  19 

Udden,  J.  A.,  63,  64 

Uneroded  top  of  fold,  70,  71 

United  States,  60 

United  States  Geol.  Surv.  folios,  48 

Unsymmetrical   anticline,    5,  6,   40,  42, 

45,  46 
Upland,  24 
Uplifts,  8 1 
Upper  Devonian,  28 
Uptilting  of  lake  region,  78,  79,  82 
Utica  shale,  25 

VanHise,  C.  R.,  9,  16,  21;  51 
Van  Horn,  F.  R.,  50,  62,  70 


Vanuxem,  L.,  36,  37,  53 
Vertical  pressure,  59 
Viola  limestone,  18 

Wallis,  B.  F.,  18 

Walnut  Creek,  24,  34,  38,  46,  61 

Warren  folio,  30 

Washita  River,  20 

Weathering,  a  cause  of  folding,  52,  82 

West  Canada  Creek,  73 

West  Virginia,  3 

Westfield,  4,  35,  39 

Wheelock,  C.  E.,  55 

White,  I.  C.,  23,  25,  27,  28,  29,  30,  31, 

4i,  63 

White,  T.  G.,  36 
Whittlesey,  35 

Wichita  Mountains,  3,  14,  17,  21,  67 
Width  of  folds,  76 
Willis,  Bailey,  7,  9,  43,  46,  76 
Wilson,  A.  W.  G.,  48 
Wisconsin,  3 
Wiscony  shale,  28 
Wood  worth,  J.  B.,  41,  69 
Worthington  peneplain,  33 
Wyoming,  12,  13 


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